I first saw the aquatic iguana (Norops aquaticus) in the southern part of Costa Rica in 1994. These lizards swam and dove in a fast-flowing stream, catching water insects. But when I told a herpetologist friend about it, she refused to believe me.
It took me 13 years to find the aquatic iguana again, and this time I had a camera with me. It was in a different part of Costa Rica (Est. Pitilla in Guanacaste), but the animal and its habitat were the same. I watched it for a couple of hours, following the lizard among slippery boulders, hoping to document its hunting behavior. Eventually I got lucky, but alas, the actual catching of the prey happened underwater, when the iguana cornered a nymph of an aquatic blattodean (a yet undescribed species.) Next time I will definitely try to get a photo of the underwater action.
Update (2 Sept 12): Turns out that the aquatic Norops iguanas that I saw in southern Costa Rica and those from the northern part of the country, shown here, are different species. The animal in the photos is Norops oxylophus, not N. aquaticus. You can read more about the amazing aquatic behavior of N. oxylophus here. (Thanks to Annemare Rijnbeek for pointing me in the right direction regarding the ID of these animals.)
Incidentally, it appears that these lizards are once again being placed in the genus Anolis, where they historically belonged.
The Smaller Majority 
Well, I know both Anolis aquaticus and Anolis lionotus (which is also called Anolis oxylophus which is considered the appropiate name) and this particular animal has characters of both. The orange dewlap and white sideline are more reminiscent of A. oxylophus, indeed. A. oxylophus is however a mostly atlantic species with just a few pacific locations in CR. But the form of the head and some aspects of coloration remind me of A. aquaticus (which is a predominantly pacific species)
Hi, the species you have photographed is not aquaticus but a lionotus. A different aquatic species.
Thanks for the tip, much appreciated.
Okay, not only are there stream aquatic lizards, but there are aquatic /cockroaches/. My mind is blown.
Fascinating post as always, Piotr. Are these related to anoles? (in the second photo it looks like the lizard has the dewlap typical to anoles). Also a technical question – are all these photos from the same hunting event? Sounds like the lizard is a relatively slow predator if you managed to change lenses between shots.
Enjoy the Galapagos!
Yes, they are anoles, and the males have an orange dewlap. These photos are of the same event; the lizard was very fast, but it took him a while to swallow the insect, which allowed me to change the lens.