Together with an expected overall decline in summer precipitation, these changes could lengthen the periods of low flow in summer, although elsewhere there are expectations of higher summer rainfall. Where intensive rainfall events become stronger and more frequent, greater flushing of diffuse agricultural pollutants to both surface water and groundwater could result, and the frequency and severity of polluted urban siormflows could increase. Overall increases in annual rainfall could have the effect of diluting diffuse pollutants. Joint EEA-JRC-WHO report. Rising water temperatures will increase the likelihood of cyanobactcrial blooms, and hotter and drier summers would deplete river (lows, reduce dilution capacity and lead to higher pollutant concentrations and possibly fish deaths (temperatures above 25°C can be fatal).