An ancient marsh at the Hammock estuary sits above layers of peat forty feet deep. Once an inland freshwater lake, it is now flooded twice daily by nutrient-rich salt tides. Tidal salt marshes filter pollutants from upland areas draining into them, protect against storm surges and rising sea levels, and support an interdependent web of micro-organisms, plants, fish, crustaceans, birds, and mammals. Osprey, once endangered, now return each year to nest and raise their young. From the town's earliest settlement in 1663, locals harvested abundant Spartina marsh grass, or salt hay, which colonists used for livestock food and bedding and for winter insulation in their homes. In the Hammock River, east of the nearby Beach Park Road bridge, the remaining stones of a 1697 sluice gate and cart road can still be seen at low tide; one of only two such structures known in Connecticut, it was built after five Killinworth residents—John Kelsie, Will Barber, Will Stephens, Robert Lane, and Peter Farnam—successfully petitioned colonial authorities in Hartford for the right to construct it, with costs paid by those who benefited. The sluice gate controlled tidal flow into the marshes, and the cart road improved access for harvesting salt hay. In 2006, the Richards family donated over 50 acres of this pristine salt marsh to the Clinton Land Conservation Trust to preserve it for the enjoyment of all.