COLUMBUS, Ohio (AP) — Ohio officials say a first-ever comprehensive study of the state’s largest rivers indicates great improvement in water quality over the past few decades.

Gov. Mike DeWine and state environmental protection officials said Tuesday that the study concluded that 86% of the miles of Ohio’s large rivers surveyed were in good to excellent condition, up from only 18% in the 1980s.

The “Aquatic Life and Water Quality Survey of Ohio’s Large Rivers” done by the Ohio Environmental Protection Agency called this “dramatic reversal” the result of improved wastewater infrastructure and treatment as well as agricultural soil conservation measures.

The report found major reductions in ammonia, total phosphorous and lead in water chemistry as well as reductions in PCBs and mercury, lead, cadmium, arsenic and other metals in fish. It said “legacy pollution” from coal mining and heavy industry is still detectible in water and sediment “but causes only modest impact to aquatic life.”

Only the Mohican River showed a significant decline in water quality due to excessive levels of phosphorus and nutrients from agricultural runoff. The study also found, however, that Ohio’s large rivers have been warming over each of the past few decades.

Bob Miltner, a senior scientist with the Ohio EPA and the study’s lead author, said there’s still work to be done to mitigate the impacts of algae blooms, the Columbus Dispatch reported.

Amid concern about such blooms in Lake Erie and surrounding waterways due to elevated levels of phosphorus and nitrogen, Ohio, Michigan and Ontario committed in 2015 to reduce phosphorus inputs by 40% over the next decade. Recent research, however, indicates that neither Ohio nor Michigan will meet that goal and will need more funding, the newspaper reported.

Because phosphorus and nitrogen are commonly found in fertilizer and human waste, DeWine said Tuesday that officials plan to work with farmers and modernize stormwater management systems to try to reduce the problem, the Dispatch reported.