say that due to erosion, the Cape will be completely submerged by the sea within several thousand years. This erosion causes the washout of beaches and the destruction of the barrier islands; for example, the ocean broke through the barrier island at Chatham during Hurricane Bob in 1991, allowing waves and storm surges to hit the coast with no obstruction. Consequently, the sediment and sand from the beaches is being washed away and deposited elsewhere. While this destroys land in some places, it creates land elsewhere, most noticeably in marshes where sediment is deposited by flowing water. Cape Cod's aquifer consists of six hydrologically independent lenses from which all the towns on the Cape obtain drinking water (except Falmouth, which, in 2015, drew 43.5% of its water from Long Pond). Contamination with industrial chemicals and pharmaceutical drugs from septic systems is a concern. Climate Under the Koppen Climate Classification, the Cape Cod area has a temperate humid climate or Cfb climate (coldest month has a mean temperature above -3 C (26.4 F) but below 18 C (64.4 F). Locally, the Cape has a more moderate climate than inland locations in eastern New England. On occasion it takes the brunt of extreme weather systems such as the Blizzard of 2005 and Hurricane Bob. Because of the influence of the Atlantic Ocean on three sides, temperatures are typically a few degrees lower in the summer and often several degrees higher in the winter than the adjacent mainland. Two ocean currents (the Gulf Stream, a warm ocean current from the south) and the Labrador Current, a cold ocean current from the north), meander and interact with each other. As a result, the ocean temperatures on the eastern shore of Cape Cod rarely gets above , while along the southern coast (Nantucket Sound), water temperatures can sometimes reach or higher. Cape Cod's climate is also known for a delayed spring season due to the sea remaining cold from the winter; by the same token, the summer heat retained in the sea moderates fall temperatures in comparison to the adjacent inland area. The highest temperature yet recorded on the peninsula was in Provincetown,; the lowest temperature recorded was in Barnstable. The water surrounding Cape Cod moderates winter temperatures nearly enough to extend the humid subtropical climate zone to what could be its northernmost limit in eastern North America, as the majority of Cape Cod is