Best and Worst Waters for Anglers: National Study Ranks Major US Fishing Destinations

Lake Okeechobee in Florida is America’s dirtiest lake. 0.67 µg/L of lead was detected in its most recent samples. There is no safe level of lead and its presence in lakes is unnatural. Turbidity here was the second-highest of all evaluated lakes, measuring 34.36 NTU, after Utah Lake’s 58.11 NTU. This gives the impression of rather cloudy water. One cause for the murky appearance of Lake Okeechobee may be the high levels of phosphorus, estimated at 0.18 mg/L, which stimulates algae growth.

American Falls Reservoir in Idaho is the second dirtiest lake in the US. This 88-square-mile man-made reservoir appears clear to the human eye, at first, considering its turbidity levels measure a reasonable 8 NTU. However, chemical tests concluded it contained ammonia, which should not be present at all, estimated at 0.15 mg/L. When ammonia levels reach 0.53 mg/L, the water becomes harmful to fish. 

Lake Texoma ranked third worst for cleanliness. Bordering Texas and Oklahoma, this reservoir is quite poorly oxygenated, solids-heavy and has a subtle rotten egg smell. Dissolved oxygen here is only 4.42 mg/L – if it were to drop below 2 mg/L, Lake Texoma would become hypoxic, meaning fish would suffocate. Sulfates of 164.05 mg/L, which are the fourth worst of all studied lakes, give the water an unpleasant odor. Lake Texoma has the fifth highest levels of TDS, estimated at 753.59 mg/L. 

The absolute worst levels of TDS are recorded at the Pyramid Lake in Nevada, where they reach 5,488 mg/L. This is also where the pH deviates the most from the ideal level of 7 for lakes, with the last reading taken on February 12, 2020, showing an average pH level of 9.36.

Lake of the Woods, stretching across Canada’s Manitoba and Ontario provinces and into Minnesota, is the most lead-contaminated lake of the 100 included in the study. A sample taken on August 16, 2022, detected lead levels of 1 µg/L.

Devils Lake in North Dakota is the smelliest of all, where sulfate concentrations reach 745.17 mg/L. This may have happened due to its glacial deposits building up over thousands of years, with no natural outlet to dilute these sulfates over time. 

Serge Selezen, CEO of Fishbox, commented on the findings:

“The health of fish populations is directly tied to water quality, and this data reveals some concerning trends. Dissolved oxygen is the most critical factor – when levels drop below 5 mg/L, fish become stressed, and below 2 mg/L, waters become hypoxic and can’t support most fish life.

“On average, America’s largest lakes have an acceptable pH balance of 7.96, good turbidity levels of 9.54 NTU, and healthy dissolved oxygen of 7.29 mg/L. They do, however, have quite significant TDS of 504.05 mg/L, a ninth of which (57.15 mg/L) comprise sulfates. Phosphorus levels average 0.05 mg/L. Ammonia was spotted in 24 lakes averaging 0.096 mg/L and lead – in 11, averaging 0.367 mg/L.

“We are pleased to find that, generally speaking, large lakes remain very clean and safe to swim and fish in, though monitoring any signage near swimming spots and adhering to the indicated advice may save you from catching a rare but nasty stomach bug.

“For anglers and anyone concerned about freshwater ecosystems, these numbers should serve as a wake-up call. Clean water isn’t just about human recreation, it’s about maintaining the delicate balance that keeps our fish populations thriving.”

Sources: 

Fishbox via the National Water Quality Monitoring Council.

Methodology:

1.    This study uses data from waterqualitydata.us to rank the 100 largest US lakes by surface area based on how dirty they are. 

2.    Each lake was ranked using a score calculated with the following equally weighed factors:

• Dissolved Oxygen Concentration;
• Ammonia Concentration;
• Lead Concentration;
• Phosphorus Concentration;
• Sulfate Concentration;
• Total Dissolved Solids;
• Turbidity;
• Difference from pH of 7.

3.    The researchers used the latest available figures for each indicator, reported up until July 15th, 2025.

4.    Lakes with less than three factors available in the official data were excluded, resulting in a list of 46 of the largest lakes in the US whose cleanliness could be accurately measured.