Those are key findings of a just-released report from Otago Fish & Game, which also wants the Otago Regional Council to ramp up its monitoring and compliance work.
Otago Fish & Game officer Morgan Trotter said sediment pollution damaged fish and other aquatic life and had been a ''growing concern'' for a decade.
High winter rainfall was rapidly approaching and Fish & Game wanted to highlight the adverse impact sedimentation had on the health of rivers and streams, Mr Morgan said.
Sediment arising from run-off from paddocks, particularly during heavy rain, was a ''major stressor of stream life'', smothering invertebrate habitat and fish eggs.
Recent data, and a recent University of Otago scientific paper, showed sediment levels in many South Otago streams were ''too high, resulting in degraded aquatic ecosystems and fisheries''.
A major source of in-stream sediment was winter cropping practices such as strip grazing of stock with insufficient riparian buffers or on land that was too steep.
There were signs that intensive farming practices were improving and he praised some ''great community initiatives'', such the Pomahaka River Care Group, but more council resources were needed to tackle winter sediment run-off, he said.
Winter cropping without using a sediment-control measure was a prohibited activity, but the council needed to provide more clear guidance about what constituted acceptable controls, he said.
Council chief executive Peter Bodeker welcomed Fish & Game's ''very valuable'' report and said the council would study it to see where sediment-control improvements could be made.
The report was timely, raising awareness about the winter cropping issue as winter drew near, he said.
The council would undertake monitoring and enforcement action over the winter, including low-flying fixed-wing aircraft flights over rivers in the area to check on sediment problems.
The council would be meeting Fish & Game soon and would offer a Fish & Game representative a seat on aircraft flights.
Farmers could take some simple steps that would cost little or no money but would reduce sediment run-off.
One measure was to graze crops from the hilltops, moving the stock progressively lower around the hillsides as winter advanced.
This left an area of crop at lower levels around the hills to capture any soil runoff from higher areas, Mr Bodeker said.
