water in oil

have a 2001 4 stroke yamaha outboard and have found water in the oil... anyone know why?

What model? The most common problem is a stuck open thermostat which results in a cold running motor and condensation forms internally. The motor never gets warm enough to vaporize the condensation or the normally occurring blow by. That was the easy answer. The answer you hope it isn't is leaking base, oil pan, or head gaskets. Some models like the F115 had some issues with the exhaust guide warping and allowing leakage into the oil from under the powerhead area. If your motor has had a recent overheat incident be sure to check the t-stat because it can become stuck open.