New Scientist is running a gallery of orangutans interacting in water. These are orphaned orangutans that were relocated to an island and have since been observed to interact with water in all kinds of unusual ways – snatching fish, sex in water, trawling for sunken fruit.
Others in the group have found drier means of crossing water: they've learned how to build bridges. "They deliberately bend slender trees over and use them as bridges to travel over broad stretches of water," says [Anne] Russon. "The trees remain partially bent after the first use, and after several uses they stay permanently bent into these positions." And although each bridge is engineered by a single orang-utan, the structure is used by all the orang-utans on Kaja. "Nothing like this has been seen anywhere else," says Russon.
The introduction notes that these behaviors are rarely observed, and that many zoo orangutans have drowned in “moats” meant to enclose them. Several of the behaviors seem to be driven by individuals using the water to prevent competition from others.