Prospect Lake. A small lake in Memorial Park, near downtown. Not huge, but probably the largest in the city limits.
A large protected body of water
A large inland body of water is called a lake.
It will harm the large body of water.
An ocean is the largest body of water. The next largest is called a sea.
The Colorado River.
The Sea of Cortez.
the large body of water that flows across the land is a river.
What you're describing could be called an inlet, a fjord, a marsh or a sound, plus other variants. The geographical description depends on the shape of the land that surrounds the body of water. The water can be either salt water or fresh water, depending on the body of water's proximity to the sea or melting snow or springs. Please see the link, below, to learn more.
The Sea of Cortez.
The Sea of Cortez.
The Colorado River.
A plain bordered by a large body of water is called a coastal plain.