Most likely Gambusia; unfortunately the twin dams are infested with Gambusia. The Gambusia infestations were the reason why FoMM gave up trying to improve frog habitat at the dams ...
Matt. I recall a proposal (in which you were involved, I think) a few years back to eliminate gambusia from selected urban waterbodies and to refill their niche with native spp. The plan included building a stock of galaxias in volunteer backyard ponds. Did it get anywhere? Daryl