Outdoor recreation affects sediment and can increase erosion:

• When recreationalists (e.g., hikers, bikers, horseback riders and motorized vehicle users) do not use a bridge to cross waterways (rivers or creeks), they can disturb sediment and cause it to be carried downstream.  If the river or creek has an exposed stream bank, the amount of disturbed sediment can be even higher.  
• Frequently used hillside trails are at a higher risk of damage, including soil disturbance or loss of vegetation.  When this damage occurs, erosion (from rain or snowmelt) increases, contributing to higher levels of sediment in waterways.
• Vehicles with large tire treads can destroy vegetation and churn up the soil, resulting in increased erosion from rain or snowmelt.  
• Increased sediment in waterways causes difficulties for water treatment facilities.
• Increased sediment in waterways affects the habitat of fish and aquatic insects. 

Recreation increases the types and amounts of substances found in water:

• Sunscreen and insect repellent from swimmers can wash off into the water.
• Gasoline, motor oil, and other vehicular fluids can spill or leak into waterways.   
• Improperly managed sanitary waste and garbage can end up in the water.

Recreation can contribute to the problem of aquatic invasive species:

• Boats or fishing gear that are used in multiple bodies of water can transport aquatic invasive species, thereby changing ecosystems and impacting water quality.