Lake Helen.

The name of the park is different from the name of the lake.

google.com/maps/@34.619472,-98.3941414,3a,75y,69.78h,85.85t/data=!3m6!1e1!3m4!1sG7ndNwp24bQVbXJOOu2IpQ!2e0!7i13312!8i6656

The real Lake Elmer Thomas is west of Medicine Park.