Flaten is a lake

Lake

A lake is a body of relatively still fresh or salt water of considerable size, localized in a basin, that is surrounded by land. Lakes are inland and not part of the ocean and therefore are distinct from lagoons, and are larger and deeper than ponds. Lakes can be contrasted with rivers or streams,...

 in southern Stockholm

Stockholm

Stockholm is the capital and the largest city of Sweden and constitutes the most populated urban area in Scandinavia. Stockholm is the most populous city in Sweden, with a population of 851,155 in the municipality , 1.37 million in the urban area , and around 2.1 million in the metropolitan area...

, Sweden

Sweden

Sweden , officially the Kingdom of Sweden , is a Nordic country on the Scandinavian Peninsula in Northern Europe. Sweden borders with Norway and Finland and is connected to Denmark by a bridge-tunnel across the Öresund....

, located just north of Lake Drevviken. The name is also used for the surrounding area and the nature reserve

Nature reserve

A nature reserve is a protected area of importance for wildlife, flora, fauna or features of geological or other special interest, which is reserved and managed for conservation and to provide special opportunities for study or research...

 created there in 2007.

Flaten has the best water quality of all lakes around the Swedish capital and is highly popular for bathing and angling. The surrounding area is dominated by forests, with allotment-gardens

Allotment (gardening)

An allotment garden, often called simply an allotment, is a plot of land made available for individual, non-professional gardening. Such plots are formed by subdividing a piece of land into a few or up to several hundreds of land parcels that are assigned to individuals or families...

 and some industrial activities located north of the lake. Algal bloom

Algal bloom

An algal bloom is a rapid increase or accumulation in the population of algae in an aquatic system. Algal blooms may occur in freshwater as well as marine environments. Typically, only one or a small number of phytoplankton species are involved, and some blooms may be recognized by discoloration...

 occasionally occurs in spring.

Catchment area

The undulating wooded grounds of the catchment area are considered as of significant natural value and, through the location within a nature reserve and proximity to Stockholm, also of significant recreational value. A scenic ravine is found by the southern end of the lake while most nearby settlements are located north of it. The arrea is used for various open-air activities including walking, bathing, camping, canoeing, and fishing.
The area is a fine example of the fissure-valley landscape prevalent in the entire Stockholm County

Stockholm County

Stockholm County is a county or län on the Baltic sea coast of Sweden. It borders Uppsala County and Södermanland County. It also borders Mälaren and the Baltic Sea. The city of Stockholm is the capital of Sweden. Stockholm County is divided by the historic provinces of Uppland and Södermanland...

, featuring elevated flat rocks separated by valleys with oaks and spruces, some of which can be several hundreds years old. In the catchment area are also three allotment-gardens and the residential area Skarpnäck

Skarpnäck

Skarpnäck may refer to:*Skarpnäck borough in Stockholm, Sweden*Skarpnäck metro station, a Stockholm Metro station*Skarpnäck parish, a Church of Sweden parish in Stockholm, Sweden*Skarpnäcksfältet, a subdistrict in Skarpnäcks Gård district, Skarpnäck borough...

. A bathe is located on the eastern shore. The catchment area for groundwater

Groundwater

Groundwater is water located beneath the ground surface in soil pore spaces and in the fractures of rock formations. A unit of rock or an unconsolidated deposit is called an aquifer when it can yield a usable quantity of water. The depth at which soil pore spaces or fractures and voids in rock...

 is much larger than that for stormwater.

Environmental influence

In summer, when the lake is stratified, bottom layers suffer of oxygen depletion causing release of phosphorus

Phosphorus

Phosphorus is the chemical element that has the symbol P and atomic number 15. A multivalent nonmetal of the nitrogen group, phosphorus as a mineral is almost always present in its maximally oxidized state, as inorganic phosphate rocks...

. Treatment with aluminium chloride

Aluminium chloride

Aluminium chloride is the main compound of aluminium and chlorine. It is white, but samples are often contaminated with iron trichloride, giving it a yellow colour. The solid has a low melting and boiling point. It is mainly produced and consumed in the production of aluminium metal, but large...

 in 2000, however, greatly reduced the amount of leaking phosphorus. Most of the surface runoff

Surface runoff

Surface runoff is the water flow that occurs when soil is infiltrated to full capacity and excess water from rain, meltwater, or other sources flows over the land. This is a major component of the water cycle. Runoff that occurs on surfaces before reaching a channel is also called a nonpoint source...

 reaching Flaten comes from a ditch (Flatendiket) stretching a kilometre to empty in the northern end of the lake where two sedimentation

Sedimentation

Sedimentation is the tendency for particles in suspension to settle out of the fluid in which they are entrained, and come to rest against a barrier. This is due to their motion through the fluid in response to the forces acting on them: these forces can be due to gravity, centrifugal acceleration...

 basins reduces the amount of pollutants reaching the lake. The ditch also receives stormwater

Stormwater

Stormwater is water that originates during precipitation events. It may also be used to apply to water that originates with snowmelt that enters the stormwater system...

 from local settlements rich in nutrients and from the only road in the catchment area which contains metals and PAH

Polycyclic aromatic hydrocarbon

Polycyclic aromatic hydrocarbons , also known as poly-aromatic hydrocarbons or polynuclear aromatic hydrocarbons, are potent atmospheric pollutants that consist of fused aromatic rings and do not contain heteroatoms or carry substituents. Naphthalene is the simplest example of a PAH...

s. Occasionally, the ditch therefore transports waste water to the lake which the available caisson

Caisson (engineering)

In geotechnical engineering, a caisson is a retaining, watertight structure used, for example, to work on the foundations of a bridge pier, for the construction of a concrete dam, or for the repair of ships. These are constructed such that the water can be pumped out, keeping the working...

s mostly fails to treat properly. However, pipes from the bathe lead to a local sewage disposal plant, and, additionally, the catchment area was reduced by some 20 per cent in 1978 when stormwater from the graveyard Skogskyrkogården

Skogskyrkogården

Skogskyrkogården is a cemetery located in the Enskededalen district south of central Stockholm, Sweden...

 was guided past the lake, which decreased pollution but also increased lake retention time

Lake retention time

Lake retention time is a calculated quantity expressing the mean time that water spends in a particular lake. At its simplest this figure is the result of dividing the lake volume by the flow in or out of the lake...

.

Flora and fauna

In summers, phytoplankton

Phytoplankton

Phytoplankton are the autotrophic component of the plankton community. The name comes from the Greek words φυτόν , meaning "plant", and πλαγκτός , meaning "wanderer" or "drifter". Most phytoplankton are too small to be individually seen with the unaided eye...

 algae

Algae

Algae are a large and diverse group of simple, typically autotrophic organisms, ranging from unicellular to multicellular forms, such as the giant kelps that grow to 65 meters in length. They are photosynthetic like plants, and "simple" because their tissues are not organized into the many...

 are dominated by cyanobacteria and some carapace

Carapace

A carapace is a dorsal section of the exoskeleton or shell in a number of animal groups, including arthropods such as crustaceans and arachnids, as well as vertebrates such as turtles and tortoises. In turtles and tortoises, the underside is called the plastron.-Crustaceans:In crustaceans, the...

 flagellate

Flagellate

Flagellates are organisms with one or more whip-like organelles called flagella. Some cells in animals may be flagellate, for instance the spermatozoa of most phyla. Flowering plants do not produce flagellate cells, but ferns, mosses, green algae, some gymnosperms and other closely related plants...

s. Other species have been abundant, but today only a single nitrogen fixating algae is present in the lake. During winters and springs, Planktothrix agardhii adopt a red colour which occasionally colours the lake in shades of red and brown. Larger zooplankton

Zooplankton

Zooplankton are heterotrophic plankton. Plankton are organisms drifting in oceans, seas, and bodies of fresh water. The word "zooplankton" is derived from the Greek zoon , meaning "animal", and , meaning "wanderer" or "drifter"...

 include water fleas (Bosmina

Cladocera

Cladocera is an order of small crustaceans commonly called water fleas. Around 620 species have been recognised so far, with many more undescribed. They are ubiquitous in inland aquatic habitats, but rare in the oceans. Most are long, with a down-turned head, and a carapace covering the apparently...

) and copepod

Copepod

Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...

s (Daphnia

Daphnia

Daphnia are small, planktonic crustaceans, between 0.2 and 5 mm in length. Daphnia are members of the order Cladocera, and are one of the several small aquatic crustaceans commonly called water fleas because of their saltatory swimming style...

); and smaller species, rotifer

Rotifer

The rotifers make up a phylum of microscopic and near-microscopic pseudocoelomate animals. They were first described by Rev. John Harris in 1696, and other forms were described by Anton van Leeuwenhoek in 1703...

s, seem to have increased during the later part of the 1990s. An inventory of aquatic plant

Aquatic plant

Aquatic plants are plants that have adapted to living in aquatic environments. They are also referred to as hydrophytes or aquatic macrophytes. These plants require special adaptations for living submerged in water, or at the water's surface. Aquatic plants can only grow in water or in soil that is...

s in 1997 resulted in a list of 13 species, most commonly Spring Quillwort, Awlwort, Shoreweed, and Needle Spike-rush. The shores of Flaten are covered with Bog-myrtle

Myrica gale

Myrica gale is a species of flowering plant in the genus Myrica, native to northern and western Europe and parts of northern North America. It is a deciduous shrub growing to 1–2 m tall. Common names include Bog Myrtle and Sweet Gale...

. Trailing plants have occasionally been abundant near the bathe.

A documentation of lake bed fauna in 1997 registered 68 species, of which 14 were freshwater Gastropods

Gastropoda

The Gastropoda or gastropods, more commonly known as snails and slugs, are a large taxonomic class within the phylum Mollusca. The class Gastropoda includes snails and slugs of all kinds and all sizes from microscopic to quite large...

 commonly found around Stockholm and 5 were Dragonflies

Dragonfly

A dragonfly is a winged insect belonging to the order Odonata, the suborder Epiprocta or, in the strict sense, the infraorder Anisoptera . It is characterized by large multifaceted eyes, two pairs of strong transparent wings, and an elongated body...

. Notable catches included European Stream Valvata

Valvatidae

Valvatidae, the valve snails, is a taxonomic family of very small freshwater snails with an operculum, aquatic gastropod mollusks.- Taxonomy :...

 (Valvata piscinalis) and Duck Mussel

Duck mussel

Duck mussel, Anodonta anatina, is a species of freshwater mussel, an aquatic bivalve mollusk in the family Unionidae, the river mussels.Synonym: Anodonta piscinalis Nilsson, 1823Subspecies:*Anodonta anatina anatina...

. Common fishes are Perch

Perch

Perch is a common name for fish of the genus Perca, freshwater gamefish belonging to the family Percidae. The perch, of which there are three species in different geographical areas, lend their name to a large order of vertebrates: the Perciformes, from the Greek perke meaning spotted, and the...

, Roach

Rutilus

Rutilus is a genus of fishes in the family Cyprinidae, commonly called roaches. Locally, the name "roach" without any further qualifiers is also used for particular species, particularly the Common Roach Rutilus (Latin for "shining, red, golden, auburn") is a genus of fishes in the family...

, and Silver Bream, with bigger variations in population for Carp bream

Carp bream

The common bream, freshwater bream, bream, bronze bream or carp bream, Abramis brama, is a European species of freshwater fish in the family Cyprinidae....

, Northern pike

Northern Pike

The northern pike , is a species of carnivorous fish of the genus Esox...

, Tench

Tench

The tench or doctor fish is a freshwater and brackish water fish of the cyprinid family found throughout Eurasia from Western Europe including the British Isles east into Asia as far as the Ob and Yenisei Rivers. It is also found in Lake Baikal...

, Bleak

Bleak

The common bleak is a small pelagic fish of the Cyprinid family. It is often referred to simply as a "bleak", though this term can refer to any species of Alburnus.-Description:...

, Ruffle

Ruffle

In sewing and dressmaking, a ruffle, frill, or furbelow is a strip of fabric, lace or ribbon tightly gathered or pleated on one edge and applied to a garment, bedding, or other textile as a form of trimming...

, and Zander

Zander

Zander is a species of fish. The scientific name is Sander lucioperca , and it is closely allied to perch. Zander are often called pike-perch as they resemble the pike with their elongated body and head, and the perch with their spiny dorsal fin. Zander are not, as is commonly believed, a pike and...

 (notwithstanding attempts to introduce the latter). Crayfish

Crayfish

Crayfish, crawfish, or crawdads – members of the superfamilies Astacoidea and Parastacoidea – are freshwater crustaceans resembling small lobsters, to which they are related...

 have been successfully introduced. 13 breeding bird couples were documented in 1994 of which the Black-throated Diver

Black-throated Diver

The Black-throated Loon is a migratory aquatic bird found in the northern hemisphere. The species is known as an Arctic Loon in North America and the Black-throated Diver in Eurasia, its current name is a compromise proposed by the International Ornithological Committee.-Taxonomy:The...

 is considered the most important, even though the species is sensitive for interference so breeding might be challenging. Four of five amphibian

Amphibian

Amphibians , are a class of vertebrate animals including animals such as toads, frogs, caecilians, and salamanders. They are characterized as non-amniote ectothermic tetrapods...

s with a natural habitat in the Stockholm area are found by the lack, as were four species of bat

Bat

Bats are mammals of the order Chiroptera "hand" and pteron "wing") whose forelimbs form webbed wings, making them the only mammals naturally capable of true and sustained flight. By contrast, other mammals said to fly, such as flying squirrels, gliding possums, and colugos, glide rather than fly,...

s.