Protecting Public Health and the Environment.
Water temperature has a profound effect on organisms that live or reproduce in the water. This is particularly true of Idaho's native coldwater fish such as salmon, bull trout, and steelhead, and some amphibians (frogs and salamanders). When water temperature becomes too high, salmon and trout suffer a variety of ill effects ranging from decreased spawning success to death. For these reasons it is important to protect the state's water from unnecessary warming.
Stream temperature is an important part of water quality because:
Elevated stream temperatures can result from both natural and human-caused events. Examples of natural influences on temperature include creeks and rivers heating if they travel long distances over terrain that can't support streamside vegetation or when fires or floods remove significant portions of riparian vegetation.
Land management (human activity) can increase stream temperatures through:
While all streams warm, the best way to keep streams as cool as possible as long as possible is to maintain their natural shading from streamside vegetation.
Federal regulations implementing the Clean Water Act call for states to adopt water quality standards that restore and maintain the chemical, physical, and biological integrity of the nation's waters. This includes criteria limiting the temperature of the water so as to protect aquatic life, some species of which are quite sensitive to changes in temperature. Concern over water temperature has come to the fore because of the listing of several stocks of salmon and bull trout as threatened or endangered species.
DEQ disagrees with EPA over acceptable criteria for temperature for Idaho water bodies. At issue is a balance between temperature that is protective of cold-water dependent species yet attainable in most waterbodies. Numerous studies and investigations have been conducted by DEQ and others to determine the impact of temperature on aquatic life in various water bodies. In April 2003, EPA Region 10 issued guidance to states and tribes in the Pacific Northwest on temperature criteria to protect endangered salmonids. Idaho participated in developing this guidance but in the end dissented on most of the recommended criteria due to reservations as to their attainability. These reservations persist to this day.
DEQ's current stream temperature standards protect aquatic life uses, the only uses that have temperature requirements. The criteria vary by and to large degree define the aquatic life uses – warm water, seasonal cold water, cold water, salmonid spawning, and bull trout (see table below). The latter two are subcategories of the cold water use. For all but bull trout, DEQ uses a pair of criteria - limiting the daily maximum and daily average temperatures.
Depending on the diurnal (day to night) temperature range in a given stream, one or the other of these paired criteria will be more limiting of the stream's warmth. Using a pair of criteria limits a broader range of stream temperturess than either alone could. For bull trout the criterion is for a seven-day rolling average of daily maximums. This rolling average regulates high temperatures while allowing a few individual days to be slightly warmer.
All temperature criteria limit the maximum permissible value for the particular measure of temperature over a year or season. Idaho’s rules allow for the exceedances of the criteria due to natural background conditions, but not due to human activities (except for a small 0.3°C human caused increase in waters that are naturally warmer than criteria). There are many waters in Idaho where temperatures naturally warmer than criteria are likely to occur; however determining these natural temperatures takes modeling of past conditions which can be difficult.
aMDMT = Maximum Daily Maximum TemperaturebMWMT = Maximum Weekly (7-day average) Maximum TemperaturecMDAT = Maximum Daily Average Temperature
DEQ is undertaking rulemaking in 2011 to revise its temperature requirements, in particular the treatment requirements at IDAPA 58.01.02.401.01.c&d and the salmonid spawning criteria at IDAPAS 58.01.02.250.f.ii
Water Quality Standards LeadDon EssigDEQ State Office1410 N. HiltonBoise, ID 83706(208) firstname.lastname@example.org
A Statistical Model for Estimating Stream Temperatures in the Salmon and Clearwater River Basins, Central Idaho (2002)
Aquatic Assemblages and Their Relation to Temperature Variables of Least-Disturbed Streams in the Salmon River Basin, Central Idaho (2001)
Water Quality StandardsEPA Actions on Proposed StandardsNumeric Water Quality CriteriaWater Body Studies & Plans