I don't know what they are, but I know they aren't mosquitoes. Mosquito larva float just below the surface tension of the water, breathing thru it. They will squirm down towards the safety of the bottom when disturbed, but they come right back up.
Those look like they live on those submerged rocks.

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3/4 to 1 1/4 ac pond LMB, SMB, PS, BG, RES, CC, YP, Bardello BG, (RBT & Blue Tilapia - seasonal).