Needham's on guard

There's one pond (that I've found so far...) on the North Tract Patuxent NWR where there are Needham's skimmers and a fine collection of water lilies (the background here).  That has me wondering if there's a connection between the very shallow, very marshy, no fish pond and the presence of this particular DF, since many of the other ponds on the refuge are deeper, have fish and don't have water lilies (only spatterdock).  (7D2, 100 - 400 mm IS II @ 400 mm, 1/250 s, f/11, iso 400, tripod)