Freshwater flows surged into the Bay at the highest level in five years during March, according to the U.S. Geological Survey, perhaps signaling a return to poorer water quality in the Chesapeake after four drier-than-normal years.

Fueled by rain and snowmelt, the average flow into the Bay during March was 222,400 cubic feet per second, according to the USGS. That was 49 percent above average for the month, and the highest freshwater flow into the Bay since March 1998, when flows averaged 223,100 cfs, according to USGS figures.

Higher-than-normal streamflows usually carry larger amounts of nutrients and sediment into the Chesapeake.

Scientists were already expecting a surge in nutrients because last year’s drought meant that crops grew poorly and did not use all of the nutrients that were applied, leaving the excess ready to be flushed off the land.

In addition, heavy snows during the winter typically carry large amounts of nitrogen, as snow more effectively filters nitrogen oxides and other pollutants from the air than rain. When the snow melts in the spring, it runs into streams before there is much biological activity to soak up the nitrogen.

Final April figures were not available when the Bay Journal went to press, but figures showed higher-than-normal flows were continuing during the month.

Increased flows and nutrients typically result in algae blooms in the Bay which, along with sediment flushed off the land, cloud the water and prevent sunlight from reaching underwater Bay grass beds.

The grasses thrived during recent low-flow years, but could suffer a setback because of this year’s flows.

When the excess algae die, they sink to the bottom and decompose in a process that depletes deep water areas of oxygen.

But the news isn’t all bad: Oysters may benefit as the freshwater flows may push back the diseases that have devastated the Bay’s native oyster population in recent years. The diseases thrived in the high-salinity water which has filled the Bay during droughts of the past two years, sending the Bay’s oyster population to the lowest level on record.