A healthy river system is one that is in equilibrium the sediment is in balance between erosion in high-energy areas and deposition in other areas without too little or too much sediment. The removal of suspended sediment accounts for a large portion of the cost to treat water for public consumption, and can be devastating for spawning of various fish species. Sediment can clog or irritate fish gills, so that they are unable to function. Different fish species prefer different size spawning gravels, which can be covered by finer sediment from soil erosion. Sediment can also smother eggs once they have been laid, and can smother the aquatic nymphs of many invertebrate species such and stoneflies and mayflies.
Erosion is a natural process, but can be sped up by clearing land for development and agriculture.
A typical construction site can erode at a rate up to 100,000 tons per square mile per year, and can damage up to three miles of waterway below the site. In contrast, forest land erodes at rates up to 50 tons per square mile per year, and agricultural crop land erodes up to 500 tons per square mile per year. Livestock grazing and other disturbances along rivers destroys the riverbank s ability to dissipate the energy of falling raindrops and their erosive power, and destroys the water storing capabilities of vegetated areas along streams. This increases erosion 8-110 times, can contribute to the loss of valuable topsoil, and can increase flooding downstream. Runoff from roads can also be a significant source of sediment to streams, and can become a problem on small streams with little capacity for flushing, and in wetlands and shallow ponds.