Oakwood Local Rules state that all lakes are lateral penalty areas. The margin being the water side of the perimeter cement curb or wooden barrier. The curb or wood piles around the area are immoveable obstructions and you may take free relief of one club-length.
If your ball is near the water’s edge but not touching these barriers, you may need to take penalty relief (Rule 17.1) to get you safely away from the water’s edge. That would be lateral relief – 2 club lengths, no closer to the hole, one penalty stroke.