Vasai Creek is an estuarine

Estuary

An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the open sea....

 creek, one of the two main distributaries

Distributary

A distributary, or a distributary channel, is a stream that branches off and flows away from a main stream channel. They are a common feature of river deltas. The phenomenon is known as river bifurcation. The opposite of a distributary is a tributary...

 of the Ulhas River

Ulhas River

The Ulhas River is a river of western India. It originates near Karjat in the Western Ghats Range, and flows westward through Raigad and Thane districts of Maharashtra between Kulgaon-Badlapur, north to Ulhasnagar and on to Kalyan, where it turns west to Thane...

 in Maharashtra

Maharashtra

Maharashtra is a state located in India. It is the second most populous after Uttar Pradesh and third largest state by area in India...

 state of western India

India

India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...

. The Ulhas splits at the northeast corner of Salsette Island into its two main distributaries, Vasai Creek and Thane Creek

Thane Creek

Thane Creek is part of the estuary of the Ulhas River in western India opening into Mumbai Harbour. It comprises the area stretching from Mumbra Retibunder to the Mankhurd-Vashi Bridge. It has been recognised as an Important Bird Area by the Bombay Natural History Society, as it is home to...

. Vasai Creek forms the northern boundary of Salsette Island, and empties west into the Arabian Sea

Arabian Sea

The Arabian Sea is a region of the Indian Ocean bounded on the east by India, on the north by Pakistan and Iran, on the west by the Arabian Peninsula, on the south, approximately, by a line between Cape Guardafui in northeastern Somalia and Kanyakumari in India...

; Thane creek empties southwards into Bombay Harbour.