<P> In an earlier time, one person had described the transparency of the water: "I remember the time, gentlemen, when you could go in twelve feet of water and you could see the pebbles on the bottom of this river ." As the water got more polluted, it darkened, underwater vegetation (such as photosynthesizing seagrass) began dying, and as the seagrass beds declined, the many associated species of their ecosystems declined as well, contributing to the decline of the river . Also harmful was the general destruction of the once plentiful oyster beds in the waters around the city, and the over-fishing of menhaden, or mossbunker, a small silvery fish which had been used since the time of the Native Americans for fertilizing crops - however it took 8,000 of these schooling fish to fertilize a single acre, so mechanized fishing using the purse seine was developed, and eventually the menhaden population collapsed . Menhaden feed on phytoplankton, helping to keep them in check, and are also a vital step in the food chain, as bluefish, striped bass and other fish species which do not eat phytoplankton feed on the menhaden . The oyster is another filter feeder: oysters purify 10 to 100 gallons a day, while each menhaden filters four gallons in a minute, and their schools were immense: one report had a farmer collecting 20 oxcarts worth of menhaden using simple fishing nets deployed from the shore . The combination of more sewage, due to the availability of more potable water--New York's water consumption per capita was twice that of Europe--indoor plumbing, the destruction of filter feeders, and the collapse of the food chain, damaged the ecosystem of the waters around New York, including the East River, almost beyond repair . </P> <P> Because of these changes to the ecosystem, by 1909, the level of dissolved - oxygen in the lower part of the river had declined to less than 65%, where 55% of saturation is the point at which the amount of fish and the number of their species begins to be affected . Only 17 years later, by 1926, the level of dissolved oxygen in the river had fallen to 13%, below the point at which most fish species can survive . </P> <P> Due to heavy pollution, the East River is dangerous to people who fall in or attempt to swim in it, although as of mid-2007 the water was cleaner than it had been in decades . As of 2010, the New York City Department of Environmental Protection (DEP) categorizes the East River as Use Classification I, meaning it is safe for secondary contact activities such as boating and fishing . According to the marine sciences section of the DEP, the channel is swift, with water moving as fast as four knots, just as it does in the Hudson River on the other side of Manhattan . That speed can push casual swimmers out to sea . A few people drown in the waters around New York City each year . </P> <P> As of 2013, it was reported that the level of bacteria in the river was below Federal guidelines for swimming on most days, although the readings may vary significantly, so that the outflow from Newtown Creek or the Gowanus Canal can be tens or hundreds of times higher than recommended, according to Riverkeeper, a non-profit environmentalist advocacy group . The counts are also higher along the shores of the strait than they are in the middle of its flow . Nevertheless, the "Brooklyn Bridge Swim" is an annual event where swimmers cross the channel from Brooklyn Bridge Park to Manhattan . </P>

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