I believe this bug that we saw swimming along the margin of a submerged boulder in Millard Canyon Creek (Angeles National Forest at ~1600 foot elevation, in the Altadena foothills, CA) is some form of giant water bug (toe biter), but it looked slightly smaller with a shinier carapace than most giant water bugs I’ve seen. It was about 1.5 inches long. Can you identify it for me? We left it puttering around in a fairly still, algae-filled pool in the shallow creek. Buggy Best Wishes!
Not a Giant Water Bug, but a Beetle. Eric Eaton corrected us on this by writing in:”Hi, Daniel: The Predaceous Diving Beetle” is actually a Giant Water Scavenger Beetle, probably Hydrophilus triangularis. Dytiscids that large are usually outlined in yellow, which is one way I tell them apart. Hope all else is going well! Take care. Eric ”