Threats to Water Resources

Nitrogen is transported by air currents from farms and towns to remote mountain lakes and is deposited by precipitation and as dry particles.

NPS / Michael Warner

Air Pollution and Contaminants

By far, the single biggest threat to the parks’ water quality is air pollution. Air pollution adds acidic deposition, nutrients, and other contaminants to the parks’ waters. Acidic deposition is most acute as episodic events during early snowmelt and during late-summer and fall thunderstorms. Fortunately, at current levels, the parks’ waters are not showing chronic acidification, but this could change because the waters are poorly buffered and therefore limited in their capacity to neutralize acids. Because the parks’ waters are naturally low in nutrients, the addition of airborne nitrates and ammonia can cause notable changes to some lakes, such as causing an increase in algae (small green aquatic plant) growth. Algae can reduce water clarity, and the amount of dissolved oxygen available for aquatic animals.

The drift of pesticides and other contaminants from upwind agricultural areas is one of our most serious concerns. We know that measurable amounts of pesticides fall on the park, and that pesticides have been found in the tissues of aquatic fauna. We suspect that the extirpation of one species in Sequoia National Park may be linked to pesticide drift—foothill yellow-legged frog. Learn more about park air quality.

 

Middle Fork of Kaweah River at high flow after a series of extreme winter storms, outside the main entrance of Sequoia National Park, March 10, 2023. Climate change impacts are bringing more extremes - from hotter droughts to very wet winters and flooding.

NPS / Tony Caprio

Climate Change

A trend of increasing air temperature related to climate change is affecting river flow through its impact on snow accumulation and melt. Warmer air temperatures cause the rain-snow transition zone to move up in elevation, so more precipitation falls as rain, and less as snow. Less snow means less water storage in the snowpack, and reduced meltwater to feed water flows in rivers and streams. In addition, more erratic winter flows and extreme flood events, prolonged low summer flows, and reduced soil moisture are already being observed as we experience extremes of severe droughts to years of very high precipitation and flooding (such as 2023). See the Rivers, Snow, and Hydrology web page for more information.

 

Alteration of Fire Regime

The alteration of the historic fire regime by over a century of fire exclusion through grazing activity and fire suppression is another stressor to the parks’ waters. Fire affects the quantity of water in streams and its water chemistry. Sediment transport rates are different in burned and unburned watersheds. Fire affects nutrients, buffering capacity, water temperature, and other water characteristics. Visit our Fire Ecology & Research web page to learn more about fire history and fire effects monitoring.

 

Park lakes are popular destinations. Backpacker hikes toward Crabtree Pass in Sequoia National Park. Camping a good distance from water and avoiding using soap and sunscreen in park lakes can help protect water quality.

NPS / Marisa Monroe

Human Use of Park Water

Park facilities generate sewage effluent. This water contains high concentrations of nutrients. In addition to sewage effluent, there are probably other unwanted chemicals entering the parks’ waters from roads and parking lots. These have not been investigated within the parks, but they are known to be serious problems in urban areas.

Backcountry use is another source of pollutants in park waters. In areas that routinely see large concentrations of backcountry users, human feces can be a problem. Although human waste is required to be buried in the parks’ backcountry, in areas of high use, water percolating through the feces-contaminated soil eventually enters the streams and lakes. Other ways that backcountry visitors may be adding unwanted chemicals to water include misuse of soap or by swimming in lakes and streams when their bodies are covered in sunblock and insect repellent. Because the water contains so few natural dissolved constituents, the contribution of exotic chemicals on human bodies may be significant.

Exotic Species

Non-native bullfrogs and numerous fish introduced to park lakes have had detrimental effects on many native aquatic wildlife species.