Hard to answer for sure. I can tell you that we test our private well water yearly and our quality is very high. And no one I know of in the area has any quality issues. The parks should be using the same aquifer.
On the other hand these signs warning of nitrates, and warning pregnant women or infants to not use the water, have been up at CamRock since we moved here 15 years ago.
When I inquired about it years ago I was told that there may or may not be an issue with the water. It is cheaper and simpler for DCP to just post signs to be on the safe side. I am not sure if they even go through the hassle and expense to test it.