Just because the Environment Ministry says it's OK to swim in certain swimming spots doesn't mean it is completely safe.
The ministry's recent report on water quality in swimming spots tells only half the story as the results relate only to E coli levels, a regional council expert says.
Other factors such as algal blooms like cyanobacteria which can be fatal to dogs and serious for humans need to be considered.
Rangitikei's Dudding Lake was classed in the report as safe to swim in but each year the popular recreational lake succumbs to the effect of cyanobacteria, leaving it unsuitable for swimming in.
The algal bloom got so bad two years ago a triathlon event had to be moved.
Horizons water expert Barry Gilliland said lakes needed to be watched as runoff that enters them can stay there if there is no outflow.
"Which is the case for Dudding."
Mr Gilliland said that while the ministry's report was spot-on for E. coli other factors needed to be looked at to get a good overall picture of health.
"There is a lot more to look at than E. coli."
Mr Gilliland said there were a few rules to follow when it came to swimming in rivers and lakes.
"If the weather has been clear for three days before you want to swim the chances are the water is OK. But if there is a musty smell around a lake it could be a sign that cyanobacteria is present, even in low levels.
Each year Horizons monitors swimming spots around the region and posts its results on its website.
Lake Horowhenua which has serious health problems and is not recommended for recreational swimming did not feature in the report.
- © Fairfax NZ News
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