Diving Beetle!

This unique Beetle does not only swims but also dives under water. They are not able to breath underwater but it traps the air beneath its wings case, which it uses like a scuba tank. They are also capable of flight when out of water.

Not exactly the same species, but this video shows how Diving Beetles are capable of diving and breathing underwater :

In the picture, a nymph of Water Scorpion can be seen camouflaging in the substrate at the bottom of the stream.