With duck shooting season about to begin Horizons Regional Council has called on hunters to be careful not to spread weeds between waterways.

Cleaning equipment will help avoid the spread of unwanted freshwater pests, including the invasive algae didymo and hornwort, says Horizons biosecurity programme coordinator for plants Craig Davey.

"Once in a waterway aquatic plant fragments can disperse and grow rapidly, destroying the environmental, recreational and aesthetic values of our waterways. We are asking hunters moving between waterways to check, clean, dry any equipment that has come into contact with river or lake water – particularly decoys and boots," Davey said.

"Some freshwater pests, like didymo and lake snow, are microscopic and can be spread by a single drop of water. It is very easy to spread pests without knowing you are."

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Before leaving a waterway, hunters should check items and leave any weed or debris they find behind.

All items should then be cleaned for at least one minute with a five percent solution of biodegradable dishwashing solution.

Water absorbent materials such as boots require longer soaking times to allow thorough saturation.

"Drying will kill didymo, but even slightly moist items can harbour didymo and other microscopic pests for months. To ensure didymo cells are dead by drying, the item must be completely dry to the touch, inside and out, then left dry for at least another 48 hours before use," Davey said.

"Following these simple procedures will help slow freshwater pests like didymo from spreading throughout our waterways. It's everyone's responsibility to try preserve the environmental integrity of our waterways for future generations."

Duck shooting season starts on May 5.