The Hohenfelder Mühlenau is a stream, about 10 km long, in the district of Plön in northeast part of the North German state of Schleswig-Holstein

Schleswig-Holstein

Schleswig-Holstein is the northernmost of the sixteen states of Germany, comprising most of the historical duchy of Holstein and the southern part of the former Duchy of Schleswig...

.

The Hohenfelder Mühlenau is classified as a gravel-bedded stream

Stream

A stream is a body of water with a current, confined within a bed and stream banks. Depending on its locale or certain characteristics, a stream may be referred to as a branch, brook, beck, burn, creek, "crick", gill , kill, lick, rill, river, syke, bayou, rivulet, streamage, wash, run or...

. It begins at the Selenter See

Selenter See

The Selenter See is the second-largest lake in the North German state of Schleswig-Holstein, after the Großer Plöner See. It lies at an elevation of and has an area of 22.4 km²....

 in Holstein

Holstein

Holstein is the region between the rivers Elbe and Eider. It is part of Schleswig-Holstein, the northernmost state of Germany....

 and, together with the Salzau

Salzau

The Salzau is a stream, roughly 8.5 kilometres long, in the district of Plön in the North German state of Schleswig-Holstein.-Course:Together with the Mühlenau it is one of the two tailstreams of the lake known as the Selenter See. At its outlet into the Salzau near Fargau the water level of the...

 / Hagener Au

Hagener Au

The Hagener Au is a roughly long stream in the district of Plön in the north German state of Schleswig-Holstein. It is an outlet of the Passader See. From the lake's southwestern bay the stream flows in a northerly direction and discharges between Laboe and Stein in the Baltic Sea.Sections of the...

, is one of its natural tailwater

Tailwater

Tailwater refers to waters located immediately downstream from a hydraulic structure, such as a dam , bridge or culvert. Tailwater can refer to a type of fishery...

s.
The course of the stream has an incline of about 4 %, a length of 10 km, a width of generally between 2 and 4 metres and a depth of 0.1 to 1.5 metres. It is interrupted by two barriers, the mill at Köhn, which has fallen into ruins leaving just a foundation behind, and poses an obstacle of 2 to 3 metres. This hurdle will now be bypassed, in line with the EU Water Framework Directive

Water framework directive

The Water Framework Directive is a European Union directive which commits European Union member states to achieve good qualitative and quantitative status of all water bodies The Water Framework Directive (more formally the Directive 2000/60/EC of the European Parliament and of the Council of 23...

, using a drop structure

Drop structure

A drop structure, also known as a grade control, sill, or weir, is a manmade structure, typically small and built on minor streams, or as part of a dam's spillway, to pass water to a lower elevation while controlling the energy and velocity of the water as it passes over...

 (Sohlgleite) which will be built next to the existing building. The Hohenfelde Mill is another obstacle of about 4 metres, which is partly bypassed with a fish pass. The existing 50 hp Francis turbine

Francis turbine

The Francis turbine is a type of water turbine that was developed by James B. Francis in Lowell, Massachusetts. It is an inward-flow reaction turbine that combines radial and axial flow concepts....

 is still an obstacle however.
At the end of its 10 km long course the Hohenfelder Mühlenau discharges into the Baltic Sea

Baltic Sea

The Baltic Sea is a brackish mediterranean sea located in Northern Europe, from 53°N to 66°N latitude and from 20°E to 26°E longitude. It is bounded by the Scandinavian Peninsula, the mainland of Europe, and the Danish islands. It drains into the Kattegat by way of the Øresund, the Great Belt and...

 with a water quality

Water quality

Water quality is the physical, chemical and biological characteristics of water. It is a measure of the condition of water relative to the requirements of one or more biotic species and or to any human need or purpose. It is most frequently used by reference to a set of standards against which...

class of I-II.