The Save Tillson Lake group is fighting the Palisades Interstate Park Commission’s plan to remove an earthen dam, which would drain the man-made lake in Gardiner. The group was not happy that Riverkeeper, one of the most prominent environmental groups in the Hudson Valley, is supporting the plan. A Riverkeeper habitat manager argues that the plan would restore the natural flow of the Palmaghatt Kill, a tributary of the Wallkill River, which would benefit several species of fish and invertebrates.