The coordinates should lead you to a platform, overlooking the lake. As the sign says, no fishing is allowed here. Because of this, there seems to be a lot of fish in the lake, as well as turtles, frogs, waterfowl and insects like you wouldn't believe.
The cache is an Rx bottle. It contains only a vinyl log, which is best signed with a sharpie style pen. The cache can be reeled in from the platform. Please rehide out of sight.