A river, except it doesn't always have its source in the hills
Poles
river
it just flows in
Due to gravity
The water flows from various sewage systems towards the ocean.
A river.
Water flowing over a cliff is known as a waterfall, or a cataract.
An "ebb tide" flows up river, the "flow tide" flows towards the sea.
An undertow flows away from the shore, toward the open water.
The river usually flows downwards due to gravity, following the path of least resistance towards lower elevations or towards the ocean.
They originate in mountains or hills, often springing from an underground water source. Near the source there is little plant life
The name of the lake is Lake Victoria, the Nile flows towards and into the Mediterranean Sea, and the artificial lake is Lake Nasser.