Phosphate pollution chokes waterways with toxic algal blooms, but farmers need it for fertiliser.
Anglers say they have seen a major decline in fish in part of the River Eden near a sewage works.
Children from a school near a popular beauty spot test local water quality over pollution concerns.
It comes as the firm says it has completed a £26.4m project at Burstow sewage treatment works.
Previous advice not to swim in the sea off Hartlepool, Redcar, Saltburn and Marske is lifted.
The region's mayor on water, buses, women's safety and the future of public transport.
Dead eels, sticklebacks, gudgeon and stone loach were discovered in a stretch of the River Pool.
More than a dozen people are hit with vomiting and diarrhoea after swimming at Farleigh Hungerford.
The dike at Tongue Gutter wildlife site is full of sanitary towels and wet wipes, residents say.
