i want to know about public access to oxford resivour, is it legal to fish all the way around the lake if you stay in the high water mark?

Assuming you mean Oxbow Reservoir (http://fishandgame.idaho.gov/ifwis/fishingplanner/WaterInfo.aspx?qt=1&ID...) then the western half of the Reservoir is actually in Oregon so no, you cannot fish from land on the Oregon side.  Although the stateline goes down the center of the reservoir you may legally fish on any part of the water of the Reservoir and the Snake River with either a valid Idaho or Oregon fishing license.  You could legally fish from the Oregon side, but you would have to be physically in the water.