Last summer the water in Whanganui's Mowhanau Stream met swimming standards only 12 per cent of the time.

During that time there was a sewage spill from Mowhanau's wastewater treatment system and also lots of rain. Both can increase the amount of the faecal coliform bacteria, E. coli, in freshwater.

The year before swimming was good 27 per cent of the time, and in the year before that it was more than 50 per cent.

Results from the Mowhanau, Kai Iwi and Ototoka streams have shown them to be generally unsafe to swim in. The Horizons Regional Council, in conjunction with MidCentral Public Health Unit, intends to put up permanent warning signs before the swimming season begins this year.

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The situation at William Birch Pool is similar.

Although they are up and down, graphed results show bacteria levels in the Mowhanau have improved overall since 2004 when testing began.

At that time there were three dairy sheds in the Mowhanau Catchment. They discharged effluent into gullies and waterways but have since changed to land disposal.

The council has sent samples away to find out where all that E. coli comes from. For Mowhanau it is up to 50 per cent from cattle or sheep. The Kai Iwi has some from birds. For the Ototoka it is 50 to 100 per cent from cattle and sheep, especially cattle.

All the streams are at the bottom of their catchments, Horizons natural resources and partnerships manager Jon Roygard said. They collect all the run-off from source to sea.

The council has put some intensive work into the Mowhanau and Kai Iwi catchments. Waterways have been fenced off from stock, and planted.

Uptake there has been good. But the amount of E. coli bacteria from sheep and cattle in the stream shows more is needed.

"Landowners looking to do fencing and planting, they could give us a call. We are very keen to chat with landowners in that area," Roygard said.

The streams will not always be unsuitable for swimming. But people should be especially cautious if the water is running brown and discoloured, and if it has rained within the last three days.

The are advised not to put their heads under or drink the water, or to swim when they have open wounds. Young children and pregnant women need to be especially careful.

STANDARDS FOR SWIMMING WATER
+ Don't swim - 550 E. coli or more per 100ml
+ Swim with caution - 260-550 E. coli per 100ml
+ Okay to swim - less than 260 E. coli per 100ml
+ Excellent for swimming - less than 130 E. coli per 100ml

E. COLI BACTERIA
+ Found in the guts of sheep, cattle, humans, birds
+ Not usually a problem in themselves
+ Can indicate the presence of nasties like giardia

POSSIBLE EFFECTS OF SWIMMING WITH HIGH BACTERIA COUNTS
+ Sore throat
+ Sore tummy
+ Ear infection