Canberrans should conduct "visual inspections" before letting pets play in Canberra's lakes, the City Services minister says.

Tara Cheyne said ACT residents should look out for Tychonema, a species of blue-green algae suspected to have killed two dogs and made another very ill at Lake Ginninderra.

"The best thing that can be done is to avoid the water if you think there's any risk at all," Ms Cheyne told the ACT Legislative Assembly on Tuesday.

"Keep the dog away from anything that looks like fecal matter, organic matter, or something that's unusual on the shoreline.

"There is a risk that there is Tychonema in the water ... if its presence has been observed elsewhere."

Ms Cheyne said even regular testing could not be completely reliable because lake and river conditions changed so q

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