Environment Canada investigators surveying storm damage in Lanark County south of Ottawa say they have not found evidence of a tornado, but have seen tree damage consistent with powerful microbursts.

Meteorologist Peter Kimbell said the damage done during Monday's thunderstorm at cottages on the east shore of Mississippi Lake — about 60 kilometres southwest of Ottawa — was consistent with a microburst, or localized column of rapidly sinking air similar to the gust that collapsed the main stage at Ottawa's Bluesfest music festival last year.

"For the most part, it is tree damage with the trees lying in the same direction, not a long narrow corridor of damage and not a convergent pattern of damage, which we would see in a tornado," said Kimbell.

Trees near the shoreline in the area of mostly cottages were felled or uprooted with their crowns lying on the ground or on top of homes or sheds, while boats of all sizes were flung metres from where they had been moored.

Jackie McLoughlin was at work inside a marina building near the lake's shoreline when the storm hit at 4 p.m. Monday.

"The noise was deafening, the noise of the hail hitting the building — and it's a huge steel building — the noise was so strong and you couldn't see out the building," said McLoughlin. "Once it cleared up and you went outside this is what you saw, and it's devastation all along the line."

2 unconfirmed tornadoes sighted

Campers at a trailer park near Lake Doré, close to where an unconfirmed tornado was reported near Golden Lake about 140 kilometres west of Ottawa, clean up after Monday's heavy winds and rain. (CBC)

Kimbell and fellow investigator Serge Besner visited a number of eastern Ontario communities Tuesday.

There were two unconfirmed tornado sightings during Monday's storm: one in Lanark County and another further west near Golden Lake and the community of Eganville, Ont., about 140 kilometres west of Ottawa.

Kimbell and Besner were on their way to survey the damage in the Golden Lake area next.

Campers at a trailer park near Lake Doré, close to where the unconfirmed tornado near Golden Lake was sighted, said they were shaken up after heavy rain and wind hit at about 2:30 p.m. ET.

No injuries were reported, but trees fell on several trailers at the Lake Doré Tent and Trailer Park.

Thousands still without power

A map of Hydro One power outages as of Tuesday at 3 p.m. The storm knocked down trees and power lines over a wide region stretching from Barry's Bay to Cornwall. (Hydro One)

Meanwhile, thousands of Hydro One customers in eastern Ontario were still without power Tuesday afternoon. The affected outage area stretches from west of Barry's Bay to Vankleek Hill.

The federal weather agency had issued tornado warnings for several eastern Ontario communities west of Ottawa, including Smiths Falls, Lanark, Sharbot Lake, Barry's Bay, Killaloe, Renfrew, Arnprior, Calabogie and French River.

Last Tuesday, two tornadoes touched down in eastern Ontario after a similar group of storms rolled through the region.

One hit the area of Athens, near Brockville, and another touched down around Summerstown, east of Cornwall.