Fire brigade officials are warning people not to swim or take a dip after drinking alcohol.
Cleveland Fire Brigade has issued advice after an increase in call outs to people in trouble in the River Tees last two weeks.
In one incident two fire appliances and the water rescue boat were called to reports of a man in the river at 11pm.
The man, who was under the influence of alcohol, had been swimming.
Phil Lancaster, Director of Community Protection at Cleveland Fire Brigade, said: “Cooling off in rivers, canals, ponds, quarries and lakes can have deadly consequences.
“The water may look calm on the surface, but there may be strong undercurrents that could pull even a strong swimmer under.
“The water may also feel relatively warm on the surface, but just a few feet below can be icy cold even in the hot weather and can very quickly cause severe cramp and hypothermia.
“Due to these dangers, we urge you not to swim anywhere other than in purpose-built and supervised swimming pools.”
In 2015, 321 people accidently drowned in the UK.
In Hartlepool, this summer youngsters have also been warned about the dangers of jumping into the sea from Middleton Pier at Hartlepool marina.
Two boys also needed medical attention when they cut their feet and legs on glass after jumping into the marina near the bandstand on Maritime Avenue.
The fire brigade’s advice includes staying out of the water if you have been drinking, always watch your child when near water and never swim near motor boats, jet skis or other power vehicles.