Lakes age with time and have been going through a natural process of filling in over hundreds or thousands of years. Each fill in at different rates. The natural aging process in which a lake fills in with material (such as sediment and decayed organic material) and gets shallower continues as a lake progresses to a pond, pond to marsh, marsh to meadow, and meadow to dry land.
Humans can accelerate the natural lake aging process by increasing the amount of nutrients (particularly phosphorus) and sediment that would naturally flow into a lake from the watershed. Changes in how watershed land is used can result in changes in nutrient runoff into surface waters.
Phosphorus is a nutrient that all aquatic plants and animals need to survive, but in excessive quantities can have negative impacts on lake quality. The removal of natural vegetation within the watershed and the creation or expansion of surfaces that do not absorb water (called impervious surfaces), such as roofs or paved driveways, increases the amount of phosphorus reaching surface waters. Impervious surfaces do not allow rainwater or snowmelt water to sink into the ground where phosphorus can be removed by the soil. Sources of phosphorus include:
- Septic systems
- Lawn and garden fertilizers
- Washing cars and boats near the lake
- Doing laundry or bathing in the lake
- Soil erosion
- Feeding waterfowl
- Dumping/burning leaves in or near the lake
Increased phosphorus loading to a water body fertilizes the lake and can cause nuisance algal and plant growth. Algal blooms can cloud lake water and cause taste and odor issues. Excessive phosphorus can even lead to toxic blue-green algal blooms!
Learn how to NOT feed your lake here.
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