°C (20 °F) above the ambient bay temperature. Over 1,200 facilities in the United States use OTC systems as of 2014. Temperatures can be taken through remote sensing techniques to continually monitor plants' pollution. This aids in quantifying each plants' specific effects, and allows for tighter regulation of thermal pollution. Converting facilities from once-through cooling to closed-loop systems can significantly decrease the thermal pollution emitted. These systems release water at a temperature more comparable to the natural environment. Reservoirs As water stratifies within man-made dams, the temperature at the bottom drops dramatically. Many dams are constructed to release this cold water from the bottom into the natural systems. This may be mitigated by designing the dam to release warmer surface waters instead of the colder water at the bottom of the reservoir. Urban runoff During warm weather, urban runoff can have significant thermal impacts on small streams. As storm water passes over hot rooftops, parking lots, roads and sidewalks it absorbs some of the heat, an effect of the urban heat island. Storm water management facilities that absorb runoff or direct it into groundwater, such as bioretention systems and infiltration basins, reduce these thermal effects by allowing the water more time to release excess heat before entering the aquatic environment. These related systems for managing runoff are components of an expanding urban design approach commonly called green infrastructure. Retention basins (stormwater ponds) tend to be less effective at reducing runoff temperature, as the water may be heated by the sun before being discharged to a receiving stream. Effects Warm water effects Elevated temperature typically decreases the level of dissolved oxygen and of water, as gases are less soluble in hotter liquids. This can harm aquatic animals such as fish, amphibians and other aquatic organisms. Thermal pollution may also increase the metabolic rate of aquatic animals, as enzyme activity, resulting in these organisms consuming more food in a shorter time than if their environment were not changed. An increased metabolic rate may result in fewer resources; the more adapted organisms moving in may have an advantage over organisms that are not used to the warmer temperature. As a result, food chains of the old and new environments may be compromised. Some fish species will avoid stream segments or coastal areas adjacent to a thermal discharge. Biodiversity can be decreased as a result. High temperature limits oxygen dispersion into deeper waters, contributing