Yes. There is a fee to use the pools. The fee is lower for douglas county residents. Regarding the answer below, the trails are not scary and easily passable on foot.
It is a public place. I have never seen any notices that say that it is exclusive to Douglas County residents. We have never been swimming here, but we have been on the trails. Beware...other than than the paved walking path, the rest can become very muddy and one trail was like a swamp. And we saw coyotes cross the path we were on. Those trails are more suited for horses.
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