I have flown from farm ponds and it is not a problem.
When I fuel my tank I run the overflow into a collection jar. This keeps all fuel from spilling onto the ground. I fuel up on land, then start the motor still on land.
After the motor is run up I put the airplane into the water to taxy and take off.
Most all the flying is done around the pond area with only the take off and landing on the pond.

There are a lot of flying fields out there that share run way space with cows. Its not a problem.

By the way, cows do not move for airplanes.

tonyc