While visiting Kobayashi Park in University Place, WA, my children spotted a bug with long legs skating quickly over the surface of the water in a calm, off-to-the-side area of Leach Creek. After looking it up on Google, I found out the insect is called a water strider.
Wikipedia says, "Water striders can stand effortlessly on water due to their non-wetting legs. . . [they] rely on surface tension to walk on top of water. They live on the surface of ponds, slow streams, marshes, and other quiet waters. There they hunt for insects and other small invertebrates on top of or directly below surface using their strong forelegs which end with claws. They can move very quickly, up to 1.5 m/s. They paddle forward with the middle pair of their legs, using fore- and hind legs as a rudder." http://en.wikipedia.org/wiki/Water_strider
Enchanted Learning has a diagram of a water strider where you can see and learn the different parts of a water strider:
That page says that water striders do not bite people, which is good to know! :)
Here are a couple pictures. Can you see it in the pictures?
In this picture the water strider is down toward the bottom near a shadowy spot of the water. There are some neat bright reflections where it touches the water.
In this picture it's shadow can be clearly seen, but the water strider is almost the color of the sand beneath it, so it blends in and that makes it harder to see.