Metro Atlanta residents have been complaining about tap water that suddenly smells and tastes earthy or musty this fall, and water officials say they know exactly why: Lake Lanier, the main drinking water source for the region, is going through its annual autumn turnover, stirring up natural compounds and affecting systems that draw from the lake.
As reported by The Georgia Sun, algae and bacteria living in lake sediment produce two compounds, geosmin and 2-methylisoborneol, or MIB, that cause the earthy or musty smell and taste showing up in faucets this season. During summer, Lake Lanier separates into a warm upper layer and a cold lower layer, but as autumn cooling sets in, surface water gets colder and heavier and sinks, mixing the lake's bottom layers in a process known as turnover. That mixing stirs up the geosmin and MIB that settled into the sediment, and this fall, concentrations of both compounds are running higher than usual, according to the same report.
In a February 2026 episode, following resident complaints the previous week, the Gwinnett County Department of Water Resources adjusted its treatment processes, including its ozonation system, which led to a significant drop in taste and odor calls, per 11Alive. Gwinnett County's water-treatment system includes the Lanier and Shoal Creek Filter Plants, and the department serves nearly one million residents. County officials said their treatment typically handles taste and odor issues when compound levels are low, but some smell or taste may linger when geosmin and MIB peak, even though the water continues to meet all state and federal drinking water standards.
Why the Smell Is So Noticeable at Such Tiny Concentrations
The reason so many people are noticing something is off comes down to how sensitive the human nose actually is. According to Paragon Laboratories, the human nose can detect geosmin and MIB at concentrations near 5 to 10 parts per trillion, levels so minute that standard gas chromatography-mass spectrometry lab testing can be used to detect them. Federal regulators draw a clear line between that kind of aesthetic nuisance and an actual health hazard. The U.S. Environmental Protection Agency describes secondary drinking-water standards as non-enforceable guidelines for aesthetic effects such as taste and odor, distinct from primary standards that govern actual health risks.
Gwinnett County officials, per the Georgia Sun's report, said their drinking water is safe to drink, and water officials across the metro area have echoed that assessment for the broader region. Lake Lanier is the region's largest drinking-water source, according to the Atlanta Regional Commission. Every water system that draws from Lanier is experiencing the same seasonal conditions right now, and the issue typically recurs in spring as well as fall.
Utilities Ramping Up Monitoring and Treatment
Water utilities are increasing monitoring of both Lake Lanier and finished tap water, and adjusting treatment processes as conditions change, the Georgia Sun reports. Fulton County has also used activated carbon in response to elevated MIB and geosmin, while officials have assured residents that its water met safety standards. The City of Atlanta Department of Watershed Management also manually fed powdered activated carbon at its treatment plants in November 2025, according to the same station's reporting.
The stakes for getting this right go back at least a decade. In 2015, a Gwinnett County incident generated more than 950 complaints after geosmin levels in Lake Lanier climbed to 7.4 nanograms per liter, according to The Atlanta Journal-Constitution. Ozonation is part of Gwinnett's treatment system.
Longer-Term Fixes Beyond the Annual Turnover
Some of the response to the recurring problem is happening well upstream of any single treatment plant. The City of Gainesville Department of Water Resources deployed three ultrasonic MPC-Buoys in Lake Lanier in January, a chemical-free method intended to suppress algae growth, according to WSB-TV. The buoys are intended to address algae in the lake.
There's also a policy angle. Georgia lawmakers reestablished the Lake Lanier Caucus in January, according to the Chattahoochee Riverkeeper. The caucus has discussed boating safety, clean water, nutrient-pollution reduction and debris. Separately, EPD has adopted a cleanup plan related to excessive nutrient pollution. According to the University of Georgia's CAES Field Report, nutrients carried by sediment or runoff can cause eutrophication and stimulate aquatic plant growth, providing broader context for nutrient concerns in Georgia's surface waters.
For now, the message from officials up and down the Lanier supply chain remains consistent: the earthy taste making its way into glasses across Metro Atlanta is unpleasant but not unsafe, and the issue is linked to the lake's seasonal conditions.
