On average, streams and rivers were sending 133,000 cubic feet of water per second into the bay, according to the U.S. Geological Survey. That is about four times normal for August.
The previous August record was 96,000 cubic feet per second in 1955, when hurricanes Connie and Diane poured on the region.
That could have a significant impact on the health of the Chesapeake in the months to come, as freshwater flows are usually at their lowest during the summer months, USGS scientists said. The surge of precipitation this summer likely carried large amounts of nutrient and sediment pollution, and have also drastically reduced salinity in brackish bay waters.
After record July rainfall filled Chesapeake Bay waterways with trash and debris, Comptroller Peter Franchot said Maryland was "literally drowning in Pennsylvania’s trash." It's impossible to quantify how much of the detritus actually came down the Susquehanna River, but it was likely a lot.
“High river flows usually carry more pollutants into the bay and affect salinity levels, which in turn can affect oysters and fish, underwater grasses and other facets of the bay ecosystem,” USGS scientists said in a Facebook post.
River flows into the bay have remained unusually high since May, they said. Precipitation across the mid-Atlantic region this year has been up to three times normal quantities over that period, according to the National Oceanic and Atmospheric Administration.
Most of the flow is coming from the Susquehanna River and other upper bay tributaries, said Scott Phillips, the USGS Chesapeake Bay program coordinator. In recent months, a large plume of sediment has been visible across the upper bay in satellite images, he said.
Scientists are still collecting data to determine what impact the rain will have on water quality and aquatic life. Nutrient pollution could lead to decreased oxygen levels in the water. Sediment could smother underwater grasses that serve as food for waterfowl and habitat for fish and crabs. And low salinity could kill some oysters.
Tropical cyclone Florence has been downgraded to a tropical storm, but is expected to strengthen again before possibly brushing or striking the East Coast. The threat of "direct impacts associated with Florence along the U.S. East Coast next week has increased," the National Weather Service says.
Streamflow levels have declined in recent weeks, but are still above normal, he said. Whether they continue falling or surge again depends on the weather, and the threat of storms like Tropical Storm Florence, which meteorologists say could potentially reach the East Coast next week.