There have been other hard freezes through the history of the state. Most winters the Bay is open, and winter sports people must look elsewhere for amusement. Saltwater ice is formed far slower than freshwater ice and only under prolonged low temperatures. The tides and currents slow the process and the saline content of the water reduces the freezing point. Thus, the more brackish and less exposed coves freeze first.
Scientists measure the salt content of tide water in parts per thousand.
Salinity not only increases buoyancy for those whose swimming consists of floating lazily at the surface like ocean sunfish but also has much to do with the kinds of plants and animals that live beneath the surface. The Bay is salty but not overly so, becoming more and more brackish toward its head, where rivers and streams provide a freshwater mix. The Blackstone, Woonasquatucket, and Moshassuck at Providence, the Palmer River in Barrington, the Taunton at the head of Mount Hope Bay, the Pawtuxet marking the boundaries of Cranston and Warwick, and the Potowomut River in North Kingstown all play a part in reducing salinities in adjacent waters. At its entrances and for a considerable distance upward, the Bay contains water with salt content of 30 to 32 parts per thousand. The proportions drop off dramatically inside the river mouths.