Four times a day, the fury of the planet's highest tides surges in and out of the Bay of Fundy.
The gigantic ebb and flow of 100 billion tonnes of water between New Brunswick and Nova Scotia is recognized as a natural wonder -- and now, more than ever, as a massive power plant.
Canada has enough tidal energy to power most of the country's homes and the lion's share of it lies in this bay, according to Natural Resources Canada.
As early as next week, Ottawa and the government of Nova Scotia will announce whether they'll okay more development in the area -- a decision that will draw attention to the potential benefits and risks of this new source.
Only one-2,000th of that potential has been tapped so far. For 25 years, Nova Scotia has been capturing enough of the clean, renewable energy from Fundy tides to power 6,000 homes.
The 20-megawatt, tidal-power turbine on the river near Annapolis Royal is one of only two spinning in Canadian waters -- and one of only a handful in the world. The country holds more than 40 gigawatts of tidal power, although much of it lies currently beyond reach in the Arctic, far from any electrical grid.
The number of generating stations is expected to rise, especially as countries search for ways to cut back greenhouse-gas emissions.
Three companies are awaiting environmental approval from Ottawa and Nova Scotia to plunk their turbines into Fundy's inner Minas Channel. The governments could give the green light any day.
If approved, the first test unit could be in the water as early as this fall. This project could eventually lead to a larger-scale project in the Bay of Fundy, one of the most promising sites for tidal power on the planet.
But there may be a catch.
Some marine biologists warn the potential impacts of this renewable resource could devastate another resource -- the area fishery.
Mike Dadswell, a scientist who's been studying the Annapolis Royal turbine since the 1980s, said the spinning blades of the underwater powerhouse is a killing -- and maiming -- machine for marine life.
"The gulls will have a good time feeding -- there will be lots of food," said Dadswell, a fisheries and marine biology expert at Acadia University.
"Unfortunately, they're selling it on the green thing -- and everybody's so keen to do green that nobody's paying much attention, in a lot of cases, to the other problems."
Dadswell said the proposal calls for the turbines, which have blades as long as 17 metres, to be set up along the upper bay's main migration route.
It's a highway for millions of fish and it also attracts porpoises, seals and the occasional whale.
He said the equipment would essentially be anchored out in the open ocean, making them even more dangerous.
"From a green side, this isn't like a dam in the river anymore, this is windmills sitting in the sea," said Dadswell, who points out that smaller creatures can be injured by pressure generated from the swirling blades.
He fears it will be impossible to measure the damage once the turbines have been dropped out of sight, below the waves of the turbulent channel.
"It's a rough, huge-current, foggy place -- nobody does any pleasure boating out there," he said.
Dadswell is also concerned the public will forget that they're out there, making it easier for the government to give the go-ahead for more.
Politicians should instead be focusing on developing wind and solar power, he said, adding that Germany combines both to generate almost 30 per cent of the country's power.
But proponents of tidal power say ocean currents produce much more energy than wind, and with charts that predict the tides decades into the future, there is no uncertainty.
"The density of the water, the simplicity of design, the predictability of the flows makes the electricity very attractive, especially if you can find those fast-moving waters close to an electrical grid," said Glen Darou, president and CEO of Clean Current Power Systems Inc., a tidal power energy developer based in Vancouver.
Clean Current is one of the three companies chosen to test the Minas Channel. Darou insists Clean Current blades are not as threatening to larger animals because the tips are covered by a drum.
He also said the machines give off a low humming sound.
"Fish and sea mammals will sense that a long way away and they will go around it," he said.
In 2006, the company built Canada's other tidal turbine at Race Rocks Ecological Reserve, a 65-kilowatt unit off the southern tip of Vancouver Island.
Coal-dependent Nova Scotia wants 25 per cent of its energy to come from renewable sources by 2020, and it sees tidal power as a means to get there.