"Fish do not appear to be the main predators of water striders, but will in cases of starvation. Scent gland secretions from the thorax are responsible for repelling fish from eating them."
http://en.wikipedia.org/wiki/Water_strider

specific reference quoted from
Stonedahl, Lattin. 1982. The Gerridae or Water Striders of Oregon and Washington (Hemiptera:Heteroptera), Oregon State University, Pp 1-36