Concerns about drought impacts on the Bay and its resources continued to rise in March as freshwater flows seemed — in a relative sense — to barely trickle into the estuary. According to the U.S. Geological Survey, total flows into the Chesapeake averaged 34.2 billion gallons per day in February, only half the average for the month. February flows set record lows for the James and the Potomac rivers,although the Susquehanna rebounded somewhat from January lows. Last year, USGS figures showed that flows into the Bay were the lowest since 1941. Flows during the first two months of this year were below those of January and February 2001, according to USGS. With continued low rainfall in much of the watershed, March figures were also likely to be low. Low freshwater flows have greatly increased salinities in the Bay, with many areas continuing to report record highs. That’s taken a toll on oysters. Maryland officials in March reported oyster harvests this season were only about 120,000 bushels — about one third of last year’s catch — and the second-worst season on record. Scientists blamed the ongoing drought, which has allowed salinities to increase for a protracted period of time. The two diseases. which plague native oysters, thrive in high salinity conditions. High salinities were also blamed for the outbreak of a potentially harmful marine algae, Dinophysis acuminata, which turned up in the Potomac River in February. The algae forced a temporary closure of oyster beds out of concern that the algae might produce a chemical that would make humans sick. That ban was lifted after scientists concluded shellfish were not accumulating any toxic from the algae. Nonetheless, scientists said the bloom itself was persisting at unusually high densities into mid-March. Biologists were also looking ahead to see what the dry conditions would mean for the spring shad and herring runs, which begin in late March and continue through April and May. The migratory fish usually follow flows up rivers to their spawning grounds. “We presume that we need a nice spring freshet to draw fish up the Bay and pull them up the river,” said Richard St. Pierre, Susquehanna River coordinator with the U.S. Fish and Wildlife Service. “We haven’t had that yet.” But, he added, the migratory instinct is strong in fish. “They are moving upstream for a purpose, and they can find very low velocities.” A bigger concern may be the condition of the small streams that many of the fish use for spawning. With low flows in the streams, they could quickly warm and induce early spawning, which could reduce survival. “If you don’t have a lot of mixing flow out there, you could end up with 70 degree water in late April, which is not good for us,” St. Pierre said.