This is copied from the OSMB Site
Basic rule for Slow-no wake. (OAR 250-010-0025)
Operators of boats must observe Slow-no wake, maximum 5 mph speed limit within 200' of a boat ramp, marina or moorage with a capacity for six or more vessels; a floating home moorage with six or more structures; or people working at water level. Operator may be liable for damage caused by wake. This rule does not apply to commercial vessels or river navigation when more speed is needed to ensure safe passage.
Here is the link with the Paragraph:
http://www.boatoregon.com/Laws/Regs1-3.html