Corrected sentence (simple):
Fishing boats drag big nets along the bottom of the sea or through the water to catch many fish.
What I changed and why (easy steps):
- "along the bottom of the sea" is clearer than "across the bottom" — it tells where the nets move.
- "through the water" is a simple way to say "in the thick of water."
- "many fish" is a little better English than "a lot of fish." Both are okay, but "many" sounds cleaner here.
Another short version:
Fishing boats pull big nets along the seabed or through the water to catch many fish.
Small note: You typed "gramamr" — the correct spelling is "grammar." Good job asking!