When God destroyed the earth with great flood all the creatures of ground
and air were destroyed (Gen 7:22-23), but what about the creatures of
water ? Were they also destroyed?

There is no evidence in Genesis that the creatures in water
were destroyed wholesale by the flood–be they fresh or salt-water life.
It would not be surprising at all that salt water creatures were able to
survive, as their environments were effected, but not drastically. Fresh
water creatures would be able to survive a massive flood as well because,
first of all, the fresh water would flow downhill, and second, because
fresh water is considerably less dense than salt, it can exist on top of
salt water without mixing for a considerable time. There is no mention of
sea creatures being on the ark because there was no need for these animals
to find refuge there.

John Oakes