The province intentionally cut the dike — a former railway ridge — which is crumbling from the pressure of restraining the swollen creek.
A section of the 30-metre high embankment eroded and slid away on the weekend and a second slide happened on Monday, but the weakened wall is still holding back water.
There is concern, however, that it could collapse and send a massive surge of water into the valley, first through Waywayseecappo and then through to the community of Birtle.
There is a culvert at the base of the embankment but it has been plugged with ice, which forced up the level of the creek by holding back the spring runoff.
As of Monday, some of the ice appeared to be thawing, allowing water to begin streaming through, the province said.
Manitoba Infrastructure and Transportation moved equipment in Monday night and the work began at about 9 p.m., about 200 metres west of crumbling section.
Darrell Brandon, a resident of Waywayseecappo, said the crews dug down just over a metre and then placed large boulders on either side of the cut to keep the sides from eroding.
The water began flowing, slowly, at about 3:30 a.m.
"The controlled breach and pumping, combined with the slow flows from the culvert, are expected to reduce the risk of embankment failure and a surge of water flowing downstream," the province stated in a news release Tuesday morning.
"However, risk of embankment failure is still high as only the top five feet of water will be removed from behind the embankment. The situation is being monitored closely and will be updated as conditions change."
More than 100 people are out of their homes in Waywayseecappo and Birtle, where volunteers worked through the night to set up sandbag barricades.
Nancy Evans, an evacuee from Birtle, was manning the barricades in town and told CBC News the water hasn't reached there yet.
She has noticed the level of the creek has dropped, though. There is more than three metres of distance from the river to the top of the dike now, she said.
The evacuation order remains in place until tonight, when it will be reassessed by officials who will decide whether to extend it or allow people back into their homes.