In 2016, Indiana found very poor fish health in 1.27 miles of Big Branch after years of pollution. 7 years later, its fish score reached 48 and the segment was cleared

A small stream in southwestern Indiana has become a striking example of how long-term watershed restoration can reverse ecological damage. In 2016, monitoring of a 1.27-mile section of Big Branch in Sullivan County revealed a severely degraded fish community. The stream’s Index of Biotic Integrity (IBI) score was just 18, a level classified as very poor. Seven years later, follow-up monitoring produced a dramatically different result: the fish IBI had climbed to 48, rated good, while habitat quality also improved substantially. The recovery has prompted Indiana environmental officials to recommend removing the segment from the state’s impaired-waters list for 2026.

Big Branch is part of the Mud Creek–Big Branch watershed within the larger Busseron Creek watershed. The approximately four-mile stream passes through a landscape dominated by forests, farmland, hay and pasture. Indiana Department of Environmental Management monitoring had identified ecological concerns, particularly elevated turbidity and total suspended solids. Agricultural runoff and historical pollution sources contributed to the biological degradation. Although the habitat assessment in 2016 was considered good, the fish community told a different story, demonstrating why water-quality restoration cannot rely on habitat appearance alone.

The 2016 assessment found that Big Branch’s fish IBI score of 18 was far below Indiana’s minimum score of 36 for supporting biological warmwater aquatic life. That finding eventually resulted in the 1.27-mile assessment unit, identified as INB11F4_03, being placed on the Clean Water Act Section 303(d) impaired-waters list in 2018 for biological impairment. The case illustrates an important environmental lesson: a stream can possess apparently adequate physical habitat while its living communities remain under stress from pollution and runoff. Fish populations integrate multiple environmental pressures over time, making them valuable indicators of ecosystem health.


The restoration story began well before the improved fish survey. Sullivan County’s Soil and Water Conservation District started developing the Busseron Creek Watershed Management Plan in 2007, and the plan received approval in 2010 with support from Clean Water Act Section 319 funding. Subsequent phases emphasized education, outreach and financial assistance for conservation practices. Within the Mud Creek–Big Branch subwatershed, restoration included more than 1,275 acres of cover crops, nearly six acres of tree and shrub establishment, and additional upland wildlife habitat management. These measures were intended to reduce runoff and improve conditions reaching local waterways.

The broader watershed effort expanded the scale of conservation considerably. Across the Busseron Creek watershed, more than 6,300 acres of cover crops were established in priority areas, while 36 Water and Sediment Control Basin structures were installed. Nearly 4,000 acres adopted precision-agriculture tools, and more than 800 acres began using nutrient-management or no-till practices. Forty-three agricultural producers participated in best management practices, including farmers who had never previously taken part in government conservation programs. Such measures can reduce erosion, retain nutrients and slow the movement of polluted runoff toward streams.

When IDEM returned to the impaired Big Branch segment in 2023, the biological results showed how significantly conditions had changed. The fish IBI score increased from 18 to 48, comfortably exceeding Indiana’s threshold of 36. The average Qualitative Habitat Evaluation Index, or QHEI, also increased from 60 to 72, moving from good to excellent. Fish diversity rose from 11 species to 20, while the number of individual fish collected increased from 28 to 110. Perhaps most revealing, pollution-tolerant species fell from 57% of the catch to only 12%, suggesting a major shift toward a healthier fish community.

The numbers matter because fish communities provide more than a snapshot of water chemistry. According to the U.S. Environmental Protection Agency, fish assemblages—the variety and abundance of fish species in a waterbody—can reveal information about chemical, physical and biological conditions. Pollution can alter water chemistry, temperature and sediment conditions, while other human disturbances can affect aquatic ecosystems. In Big Branch, the combination of increased species diversity, greater abundance and fewer pollution-tolerant fish provides compelling evidence that the stream’s ecological condition improved rather than merely producing a temporary change in one measurement.

Big Branch’s recovery is ultimately a reminder that environmental restoration is often measured in years rather than weeks. The stream did not improve because of a single cleanup project; its progress followed years of watershed planning, agricultural conservation, technical assistance, local participation and public funding. The 2023 assessment showed the 1.27-mile segment had crossed an important biological threshold, leading IDEM to recommend its removal from the 2026 impaired-waters list. While the official record describes the status as proposed rather than simply “cleared,” the transformation from an IBI score of 18 to 48 represents a powerful conservation success story—and evidence that sustained action on land can translate into healthier life in the water.