Gates of Conowingo Dam opened in response to Hurricane Sandy

Several floodgates, four as of Thursday afternoon, were opened Thursday at the Conowingo Dam.

It's not simple move, opening the flood gates may be needed as a way of releasing pressure on the dam after Superstorm Sandy . However, the other things that come into the bay with the water have long been identified as a concern.

Officials say 80 percent of the Chesapeake Bay's pollution comes from the Conowingo Dam via the Susquehnna River. Among those -- sediment, phosphorus and nitrogen that in many ways threaten the survival of fish and other species.

According to the office of Maryland Senator EJ Pipken, a recent U.S. Geological Survey estimates that the five days proceeding Tropical Storm Lee contributed 39 percent of the suspended sediment, 22 percent of the phosphorus, and 5 percent of the nitrogen to flow through the Conowingo Dam between October 1, 2002 and September 30, 2011.

Across the environmentally fragile Chesapeake, researchers are spreading out to see what Sandy has wrought. So far, the indications are that the impact has not been as great as last fall when a pair of tropical storms caused widespread flooding that dumped mud, debris and sewage into the bay.

River flow, levels of pollutants, salinity and water clarity are among the items being measured in the bay and rivers, creeks and streams that feed the watershed.

Check back with ABC2 News as we continue to develop this story.

* The Associated Press contributed to this report.