Its average discharge of 42.2 cubic feet per second (1.19 m3/s)[1] is the most of any of the freshwater rivers on Long Island.

[2] The river rises south of NY-454 just east of the Hauppauge County Offices and flows into Blydenburgh Park Pond where other tributaries that come from East Hauppauge and Commack meet and are dammed at Blydenburgh Pond.

The river continues in a northeasterly direction, picking up additional tributaries from the north in Caleb Smith Park in Smithtown (where special regulation trout fishing is available).

Since much of the river is an estuary canoeists travel in both directions based on the tides.

Fish found in the river include Striped Bass, Bluefish, Summer Flounder, Winter Flounder, Porgies, Eels, Brown, Rainbow and Brook Trout, Yellow Perch, Largemouth Bass, Alewives, Herring, Shad, etc.