Contaminants are components of water, which do not normally occur in the concentrations found during monitoring and which render the water unsuitable or unacceptable for a specific or intended use. Constituents and parameters, on the other hand, are components or characteristics of the water system which naturally or normally occur and do not necessarily impair the water with respect to use. Constituents and parameters are used to characterize or define water quality conditions. The most widespread concerns in lakes, streams, rivers and ponds are nutrient enrichment, temperature modification and sedimentation. Review of the statistics on Montana's water bodies clearly reveals that habitat modification or the secondary effects of habitat modification are the most widespread water quality issues we have to deal with.
Habitat modification causes changes in temperature, color, sediment or nutrient solubility.
These things all affect water chemistry - nutrients, oxygen. A widespread concern in lakes, ponds and some streams is nutrient over-enrichment leading to algae blooms, plant overgrowth, oxygen deprivation, elevated temperature and changes in aquatic life. Probably the second-most common problem is sedimentation. Consequently, many monitoring programs focus some attention on depth transparency, cholorphyll a, phosphorus measurements, dissolved oxygen and temperature. Some other common measurements include pH, which is an index of acidity, total dissolved solids and alkalinity.