This year, ECan is monitoring 54 sites at rivers and lakes and 46 coastal swimming zones throughout the Canterbury region, which takes in the Waitaki catchment, including its lakes.
The first round of testing started on November 17 and results have now been posted on the ECan website, which has all sites ranked.
Two Waitaki lakes sites have ranked poor in the initial results - Lake Benmore at Glenburn and Loch Laird below the Benmore dam.
Those ranked fair were Lake Middleton (next to Lake Ohau), Lake Benmore at Sailor's Cutting, Lake Aviemore at Waitangi and the Hakataramea River at the SH82 bridge.
Lake Middleton is the only site in Canterbury which has deteriorated - from good to fair - since last season.
Good rankings have been recorded at Lake Tekapo camp beach, Lake Benmore Pumpkin Point and Lake Aviemore Te Aka.
Top rankings of very good were recorded at Lake Ruataniwha camping ground and Lake Benmore Ohau B.
In the Waimate district on the Waihao River, the popular picnic spot of Black Hole was ranked poor and Bradshaws Bridge rated fair.
ECan water portfolio chairman Mark Oldfield encouraged people to check the rankings to see how their local swimming spots were graded.
"But even good swimming sites should be avoided immediately after heavy rainfall, which can wash contaminants into the river, lake or sea," he said.
The grades are based on up to five years of monitoring data and a risk analysis of nearby potential pollution sources.
The overall grades are set in November each year and do not change during summer, although the weekly bacterial readings may vary from week to week, depending on local conditions like heavy rainfall.
The states of all sites are available on the ECan website www.ecan.govt.nz/swimming.
