Here we go again.

With three of the past five years swamping the Bay with higher than average freshwater flows - including the highest on record in 1996 - this year is already off to a wetter-than-normal start.

According to the U.S. Geological Survey, February flows into the Chesapeake were the highest ever for the month. January flows were the second highest for that month.

The February flow averaged 235,900 cubic feet per second, according to the USGS. That is about 2.2 times higher than average. Flows were particularly high in the Potomac, where their averages were about 3.8 times greater than normal.

The January flow averaged 199,700 cubic feet per second, behind only the record of 244,600 feet per second set in 1996.
After its wet start, 1996 ended up having the highest-ever flows into the Bay. Also, 1993 and 1994 were far wetter than normal.

Although figures were not yet available, the high flows almost certainly mean that huge amounts of nitrogen and phosphorus - as well as sediment - were flushed into the Bay.

Nutrient loads are closely tied to river flows because rain and snowmelt running off the land carry large amounts of nitrogen and phosphorus into local rivers and streams and, ultimately, the Bay.

High flows early in the year also tend to set up hydrologic conditions in the Bay that result in low oxygen conditions later in the year. Strong freshwater flows create a barrier between freshwater near the surface of the Bay and salt water on the bottom.

When excess algae fueled by nutrients sink to the bottom, they are decomposed by bacteria in a process that draws oxygen out of the water. The strong barrier between fresh and salt layers prevents the water from mixing and oxygen being resupplied to the bottom, resulting in oxygen-depleted "dead zones."

As a result, recent high flow events have generally resulted in large algae blooms, low oxygen conditions, and - because algae and sediment clouded the water - declines in beds of grasses which are dependent on sunlight.

But not all the news has been bad. In some years, the flows have helped set up good spawning conditions for a number of fish species, including striped bass. They also have reduced salinities in upstream parts of the Bay, which in turn helped to keep diseases away from oysters in those areas.

The timing of the flows is also critical. Although 1996 was the wettest year on record, the highest flows came in January when the ground was still frozen and water in the Bay was still cold. As a result, its impacts were not as severe as what might have been the case if the flows came later - in fact, grass beds actually expanded in 1996.

This year, flows came slightly later and temperatures were warmed. Only time will tell exactly what that means for the Chesapeake.