The crisis in Flint, Mich., and other cities offered more evidence that water contamination is a threat to human development. In the natural world, a new U.S. Geological Survey study shows, the same is true for wildlife.

Recovering from damage caused by DDT — dichlorodiphenyltrichloroethane — and PCBs — polychlorinated biphenyls, ospreys in the Chesapeake Bay are climbing back toward their historic numbers. An estimated 10,000 adult fish hawk pairs are expected to start brooding over nests with two to three eggs each next week, a far cry from the 1,500 pairs when the chemicals were widely used in the early 1970s.

DDT and PCBs built up in the fish the ospreys ate and made their egg shells so thin that adults crushed their progeny when they nested on them. The chemicals had a similar effect on eagles across America and giant condors in California before they were banned in, respectively, 1972 and 1979. As a result, ospreys have rebounded, according to a three-year study by the U.S. Geological Survey.

Researchers found that young ospreys are still exposed to PBDEs — polybrominated diphenyl ethers used in flame retardant, the USGS said. “Yet these residues had no discernible effect on the big raptors’ success in the Chesapeake region.”

There was one troubling drawback, the researchers said. “Osprey nestlings’ blood carried low levels of a biological marker for genetic damage” that was highest in the bay’s most polluted areas, such as Baltimore’s Back River wastewater treatment plant. Nearby nests fared poorly at raising chicks to adulthood.

“Baywide, the damage is not enough to affect the birds’ overall ability to reproduce, but it may be having subtle, undetected effects, and warrants more research,” said Rebecca Lazarus, a researcher at the USGS Patuxent Wildlife Research Center and the lead author of the study’s latest findings, published  in the journal Environmental Toxicology and Chemistry.

The breeding success of the bay’s most visible raptor, with its sharp golden eyes and curved talons for hooking and flying off with slippery fish, is being greeted as a conservation success after harmful chemicals were stricken from widespread use.

The bay region that covers Maryland, Virginia, West Virginia, Delaware, Pennsylvania, New York and the District is once again earning its reputation as the world’s largest breeding population for osprey pairs, what one writer dubbed “the osprey garden of the world,” according to the USGS. Last month, both chambers of the Maryland General Assembly passed bills to further limit the use of chemicals, fearing that they were affecting bees.

The two pieces of House and Senate legislation are being streamlined into a single bill for Gov. Larry Hogan to sign or reject. They would limit the household use of neonicotinoids, chemicals linked to honeybee deaths. Maryland beekeepers lost 60 percent of their colonies last year, with up to 20,000 bees each. Beekeepers who fought for the legislation are hoping bees can rebound as ospreys have.

Fish eagles are found on every continent but Antarctica, but most flock to the bay where shallow waters in tributaries make fishing easier. Ospreys recently returned to the bay from wintering in South America, prompting residents of Virginia and Maryland to train hundreds of cameras on aerial glides with six-foot wing spans and speedy descents toward prey.

“Osprey populations are thriving almost everywhere in the Chesapeake,” Lazarus said. “We found them nesting in some of the most highly contaminated areas in the bay, and we did not find any relationship between contaminants and their nests’ productivity.”

Seventy percent of the bay’s tidal waters are classified as impaired by toxic chemicals by the Environmental Protection Agency. Two of the most toxic areas in the bay are the Baltimore Harbor and the Elizabeth River in the Hampton Roads region of Virginia, said Barnett Rattner, a USGS eco-toxicologist who also helped write the study. 

“The issue with the older pesticides seems to have resolved itself,” Rattner said. “But PCBs are still there, and unfortunately their concentration really haven’t changed much in the last 30 to 40 years, showing how long lasting they are. They cause some problems in wildlife, but osprey seem to be reproducing well.”