Carrington said the weed had come up from the bottom of the lake.
Auckland Council replied to the tweet, saying the condition of the lake was "not good at all!"
"We are following up with the team who look after this issue, and we'll let you know what we find out."
An Auckland Council spokeswoman said the recent soaring temperatures were to blame.
"It is not unusual for weed growth to occur in Lake Pupuke during the hot summer conditions that we are currently experiencing.
"We have removed 25-30 tonnes of weeds from the lake recently following queries from residents and we are currently looking into options for a long-term solution to the issue."
The lake is home to the North Shore Rowing Club and Takapuna Boating Club.
Carrington is preparing for this year's Rio Olympics, where she will be looking to defend the gold medal she won in London in 2012.
She has qualified for the K1 200m and 500m events in Rio.
Carrington is the world champion in both disciplines, having won two golds at the 2015 canoe world championships in Milan.
