The mid-Atlantic drought has resulted in some of the lowest freshwater flows into the Chesapeake Bay on record, and scientists said unless rainfall returns to normal levels soon, this could soon become the most severe drought of the century.

Relief may be unlikely. Scientists at the National Oceanic and Atmospheric Administration’s National Centers for Environmental Prediction said the La Nina they blame for causing the drought will continue through the winter.

Effects of the drought, which has led to restrictions on water use throughout most of the region and caused tens of millions of dollars in crop losses, have also rippled through the Bay and its tributaries.

June freshwater flows into Bay averaged 11.2 billion gallons a day, a record low for the month, and 72 percent below average, according to the U.S. Geological Survey.

July flows averaged 8.5 billion gallons a day, 63 percent below the average of 23.1 bgd, according to the USGS, but still slightly better than the record low for the month of 6.8 bgd reported in 1966.

Scientists said the low freshwater flows into the Chesapeake were translating into record high salinities for midsummer in the Bay and its tributaries. That could be bad for oysters because high salinity helps the growth of oyster diseases such as dermo and MSX. On the other hand, saltier water helps oysters reproduce.

Also, sea nettles, which like high salinities, are being found in greater abundance, as well as farther north where Bay salinity would normally be lower.

While the abundance of sea nettles is bad news for swimmers, it could help oysters, because they eat non-stinging comb jellyfish, which eat oyster larvae.

At the same time, low flows typically mean less sediment and algae-feeding nutrients are flushed into the Bay, meaning the water is clearer. That has resulted in a rebound in Bay grasses — which took a hit during last year’s high flows — in many areas.

The drought was also blamed for the worst fish kills seen in the Bay in decades. Low oxygen conditions caused by heat and low water levels in already shallow creeks and coves resulted in kills of hundreds of thousands of fish on Maryland’s Western Shore, as well as in the Eastern Shore tributaries of both Maryland and Virginia.

Low water conditions were also stressing fish in many freshwater tributaries throughout the watershed, as they became trapped in pools where they were exposed to predators and away from shady shorelines with cooler temperatures.

“I didn’t see any dead fish, but the population was stressed for sure,” said Travis Stoe, a biologist with the Susquehanna River Basin Commission, who examined stream conditions in early August. “They are all concentrated in the pools and there is no way for them to go anywhere, in or out. That is what I found all over the place.”

Along the shore of the Chesapeake and the streams that feed it, efforts to plant seedlings that would eventually grow into runoff-filtering buffers have been harmed by the drought, as many of the trees have shriveled and died.

“We’ve been doing seedling survival checks,” said Don VanHassent, supervisor of forest stewardship for the Maryland Natural Resources Department. “Our foresters have gone out to check, and there are lots of fatalities.”

In the Bay, higher-than-normal salinities were resulting in unusual sightings in many areas. Watermen using pound nets off Hart-Miller Island, near Baltimore, have been landing red and black drum, fish that are normally seen in Tangier Sound, just north of the Virginia line. Elsewhere, crabs were reported moving into the Bush River, south of the Susquehanna, drawn by the rising salt levels, said naturalist Bob Chance.

Dolphin commonly chase their prey as far north as the Bay Bridge near Annapolis, said Cindy Driscoll, a wildlife veterinarian with the Maryland Department of Natural Resources. But this summer, boaters have seen bottlenose dolphin east of Baltimore County on Pooles Island. That is “farther north than we commonly see them,” she said.

Sightings of the world’s largest turtle, the leatherback, have increased in the Bay this year, she said.

Unusual sightings may continue as the drought could become the worst to hit the region this century, say scientists with the U.S. Geological Survey, which has been keeping such records for about 100 years.

It presently is the third-worst on record in the region, but could surpass the other two, USGS Chief Hydrologist Robert M. Hirsch told members of Congress.

“If it persists, this drought could be worse than the devastating droughts of 1929 and 1966,” Hirsch said. That will depend on whether the region gets normal amounts of rain through the fall and winter, he said.

The Associated Press contributed to this report