Question

__________ form where a river ends its journey into a still body of water like a lake or ocean.

Answer 1

The answer to your question is deltas.
Deltas may form where a river ends its journey into a still body of water like a lake or an ocean.

Answer 2

Deltas may form where a river ends its journey into a still body of water like a lake or an ocean.

I hope this helps you!! :)