Efforts to tackle agricultural pollution are not being prioritised by the Welsh Government, the chairwoman of Natural Resources Wales has said.
Diana McCrea said there had been a "continuing, unacceptable number of slurry pollution incidents".
She made her comments in a detailed letter to Environment Secretary Lesley Griffiths, saying she was "increasingly concerned and more needed to be done".
The Welsh Government said it would work with the industry to find a solution.
Soil, fertiliser and slurry from farms as well as waste from industry can find its way into rivers, killing fish and their food sources.
Ms McCrea outlined efforts being undertaken by NRW, the environmental regulator, including the establishment of a working group involving farming unions and Welsh Water.
It comes after river and fishing groups criticised the regulator's record earlier this year, claiming agricultural pollution was "out of control".
Ms McCrea said there had been 679 slurry pollution cases reported since 1 January 2010, mostly from dairy farms, ranging from about 70 to 118 a year.
NRW said it was taking some sort of action in 70% of cases.
Cautions, prosecutions and serving notices were used in those 15% of cases, which were the most serious.
She said there were good examples of the NRW and Welsh Government working well together but she was becoming "increasingly concerned that we may have lost sight of the necessary overview".
Ms McCrea, who will raise the issue at the Royal Welsh show on Monday, wants Ms Griffiths to prioritise the work of officials to help take improvements forward.
She has set out her thoughts on improving good practice on farms, inspecting slurry and silage stores while they are being built and regulating anaerobic digestion plants on farms.
Ms Griffiths is also being asked to look at allowing the use of civil sanctions to help tackle agricultural pollution, to bring Wales in line with England, but it needs the Welsh Government to pass the legislation.
A Welsh Government spokesman said Ms Griffiths would respond to the letter in due course.
He added: "Tackling agricultural pollution is crucial if we are to improve water quality in Wales.
"We look forward to working with NRW, the farming industry and other respective parties to find a solution that works for all parties."