This laid-back fishing spider (Dolomedes triton), was resting on a floating birch branch at the pond edge at the Jan Janzen Nature Centre. I had to add a tele-extender to my macro lens to get it within range, and, while holding on to a boardwalk railing, and leaning precariously over the water, I just managed to get close enough for a one-handed macro photograph. Nearby, a larger female was not as accommodating–she hid away underwater beneath the same branch, just to annoy me.
When hunting, Dolomedes spiders usually rest on the water surface, with at least one leg in contact with a stable object. They sense ripples in the water as other spiders sense prey with their webs. Fishing spiders are opportunists, feeding mostly on insects on the water surface, but the most common food item seems to be water striders (Family Gerridae)*. Dolomedes triton and other water spiders were recently featured in a study (Nyffeler M, Pusey BJ (2014) Fish Predation by Semi-Aquatic Spiders: A Global Pattern. PLoS ONE 9(6)) which examined scientific literature as well as perusing the Internet to come up with a word wide list of spiders that were capable of catching fish. Below are some images from North America: