These contraptions block the ice before they enter the channel and ram the bridge.
To stay in place in the current the best option is to stay behind the tanks.
Even in this environment you can find breathing holes though sometimes only the snorkle passes.
It's best to spot your breathing holes from the surface and make sure to have enough air to back away if you cannot fit.
For those who know Valleyfield... far, far offshore...
The air temperature was an issue. I had to pry my belt off. Total dive time was 2 hours and 20 minutes. We used 5.5 mm Dessaults.