This is a Park?
Congrats to cynig on FTF!
Yes this a park. ALthough it is not shown on the park maps, does not have a sign with a name, and is wedged between two houses, this is a park. One of many, many parks in the area! The dock at this ark provides a great view around the lake, and the park itself is generally a quiet place to stop for a few minutes. I use it as a rest stop on biking trips.
Please be careful about the private land surrounding the park. Also, since houses are nearby people may be able to see you through windows and the cahe should be found with caution!
The thing you're looking for is a black camouflaged waterproof container hidden near the waters edge. I believe I hid it when the water was high(er), so you should be able to get to it any time, although winter may bring some troubles.