Setting new thermal standards for transitional and coastal (TraC) waters

► The paper is a response to their being no previously accepted thermal standards for discharges to estuaries and coastal waters. ► We review the nature of discharges and hydrographic conditions related to the discharges in estuaries and coastal waters. ► We review the thermal requirement of key biota including fish. ► We make specific recommendations for standards which will protect key species and habitats. The construction of a new generation of coastal power stations in the UK and other western European countries has highlighted the absence of robust standards for thermal discharges to transitional and coastal waters. The proposed discharge volumes are greater than hitherto, yet there has been little independent critical examination of their potential impact, whilst much of the existing guidance has been adapted from freshwater practice. This review considers the available knowledge on the tolerance and behaviour of fish and other marine biota to heated effluents. Appropriate ways are suggested of grouping fish species to reflect their sensitivity to thermal effects. The plethora of existing standards are considered and their validity assessed in a framework of predicted seawater temperature rise. Those species or groups of organisms most likely to be affected are identified and finally specific recommendations for thermal standards consistent with long term sustainability are proposed.