The Colorado Water Quality Control Commission gave initial approval of new standards for water temperature at its hearing on January 8 and 9, 2007 - adopting temperature standards that will protect fish in Colorado’s streams and lakes. The standards adopted define the temperature levels allowed in streams and lakes so as to protect fish and wildlife – just like standards are set for ammonia, nitrates, metals, and other measures of water quality. The default statewide standards that were approved set temperature for brook and cutthroat trout streams (generally higher elevation) at 17 degrees C maximum weekly average, and 21.2 degrees C as the maximum hourly (based on a rolling two-hour average). For rainbow trout streams (generally lower elevation), the standards were 18.2 degrees C (weekly) and 23.5 degrees C (hourly). These standards are biologically-based and will provide an important protection for Colorado's fisheries.
Significantly, the Commission adopted these standards as interim protections on all 1st, 2nd, and 3rd order streams above 7000 feet elevation, and for all of the Division of Wildlife's Gold Medal waters. This provides immediate protection for much of the most important habitat for trout in Colorado, though some streams (such as the Eagle) will not be covered by the new standards until their basin-specific hearing takes place. These hearings will be completed for all portions of the state over the next five years. The first hearing will take place next year for the Colorado River basin.
More background on this issue appears below:
Why do we need standards?
Unlike humans, fish can’t regulate their own temperature. Instead, the temperature of the streams and lakes where they live controls their metabolism and determines whether they’ll live or die, and if they live, whether they’ll reproduce or grow. Changes in stream temperature happen naturally – for example, a hot summer month can elevate stream temperatures. These are stressful times for fish, especially coldwater fish like trout. But cooler nights and pockets of shaded, cooler waters give them the break they need to continue to thrive in spite of these naturally stressful conditions.
Human activity can significantly disrupt this delicate balance. Reservoir discharges of warm water, hydropower plant operations, and domestic wastewater treatment plant discharges are some of the activities that can contribute to the warming of streams. The situation can be aggravated even more by large diversions that reduce the amount of stream flows because the left over flow will heat up faster and reach higher temperatures, sometimes intolerable to fish. The combination of human activities and particularly hot summers can create situations where fish are literally left to poach in the water.
Rivers like the Fraser are at risk from elevated water temperatures.
Why is the Commission addressing temperature standards now?
Temperature was recognized as a limiting factor for fish and other aquatic life long ago. Accordingly, the Commission adopted temperature standards back in 1978. However, the standards were virtually never implemented. For example, temperature standards were included in permits authorizing discharge of treated effluent into state waters, but they were not enforced. Streams routinely evaluated for water quality standard compliance where not evaluated for temperature problems. The reason cited by the Water Quality Control Division, staff to the Commission, for not implementing the temperature standards is that the standards are unclear. For example, the standards didn’t specify how a maximum temperature was to be measured – as a daily or weekly maximum.
In 2001, the Commission convened a workgroup to discuss interpretation of the standards. A temperature standard proposal didn’t come to the Commission until 2005, but because the proposal was objected to by various industrial, water supply, and wastewater entities, the Commission postponed a final decision again. The Commission has now approved temperature standards at its January 2007 hearing.
What do these standards mean on the ground?
Like standards for zinc and other pollutants, temperature standards will be used to control discharges from facilities such as hydropower plants, wastewater treatment plants and other point sources regulated by the State. Temperature standards will also be used to evaluate impairment of streams under § 303(d) of the Clean Water Act. A determination that aquatic life use is impaired triggers a TMDL analysis and practices designed to restore the use. Federal agencies considering approval of projects that may impact instream temperature, including new or expanded water projects that will divert additional flows, will have to consider the project’s effects on instream temperature, and propose measures to prevent violation of the newly adopted standards. The State will have to consider these potential impacts and protective measures as a condition to its CWA § 401 certification of such projects.