Emergency services crews were called to Stace Place, which backs on to the open air drain, after family members reported the toddler missing shortly before 7.30pm on Saturday.

The boy was found floating in the drain, which police said was full of water and flowing quickly, about 500 metres from his home.

Members of the public had pulled the toddler from the drain as intensive care paramedics arrived.

Witnesses told paramedics the boy kept himself afloat using strokes he learned at swimming lessons.

He was treated for mild hypothermia and taken to Canberra Hospital in a stable condition.

ACT Ambulance Service duty officer Chris Barry said the boy sustained minor injuries, including scratches and bruising, after he was swept over three ledges in the waterway and came to a stop in a holding pool.

He said the boy was lucky to be alive but had reportedly been in good spirits when he was rescued.

"I'd put it down to the fact that he didn't realise the danger he was in; children often don't realise that they're in trouble," he said.

"It's very lucky it would appear he was able to swim and able to save himself."

Stace Place resident Caleb Watt, who heard distressed screams around the time the toddler went missing on Saturday night, said the stormwater drain was often dangerously full after a lot of rain.

He said he often had to stop his 15-month-old son from running towards a walkway in the cul-de-sac which led to the reserve.

"The water gets really high. This is pretty standard for a bit of rain. All the water rushes down from the mountains and hills around here and leads to the pond further down," Mr Watt said.

Royal Life Saving of Australia ACT executive director Cherry O'Connor said the incident highlighted a need to educate parents and children of the water safety issues surrounding the territory's growing number of scenic ponds and stormwater drains.

"In the ACT the stormwater drains have been integrated as features in some of our suburbs so they attract children, rather than deter them," she said.

"We've been speaking to the ACT Education and Training Directorate to incorporate a specific unit of work that addresses stormwater drains and other urban aquatic areas like urban ponds.

"We're constantly pushing for mandatory water safety for all primary school children and that would be as part of an annual program."

Ms O'Connor said the unpredictable nature of flash flooding and the large volumes of water were a major concern and parents and children could understimate how dangerous they were.

"Just stay right away," she said.

"The primary message for parents is vigilant supervision, especially children under the age of five, they need to be within arms length at all time and that's both in and around water."

Another Stace Place resident, Peri Ioannu,

But Ms O'Connor believed signs in the ACT were generally clear and effective for adults.

"I think the signage around our stormwater drains isn't too bad to be honest," she said.

Saturday's incident wasn't the first time young Canberrans have gotten into trouble in suburban stormwater drains.

The ACT Government launched an investigation into the safety of handrails at Yerrabi Pond in Gungahlin after three young girls nearly drowned when they were swept away by strong floodwaters in October 2012.

The girls were trying to cross a footbridge over a stormwater drain, which was flooded with about 30cm of water after heavy rains the day prior.

In September 2013 Shane Allen, of Calwell, rescued Jeysun Bilgin, then 13, from a flooded stormwater drain in Isabella Plains.