Growing on the edge of the pond
Is it invasive? Ok for fish?
Franklin County Ohio pond
Looks like marsh seedbox (Ludwigia palustris) or possibly some other Ludwigia spp. It can spread pretty aggressively, but is native and will confine its growth to the shoreline. It certainly poses no threat to fish and isn't likely to become excessive as cover because of its near-shore nature. Consider this link: http://plants.usda.gov/core/profile?symbol=LUPA