It was unclear why the whale had strayed so far from its natural habitat, with serious concerns raised over its chances of survival in the Seine's warmer, non-salty waters.
"Today is a big day for the beluga and all those involved in its rescue," Sea Shepherd France said in a tweet.
In the saltwater tank, the whale "will be monitored and get help, with the hope that what it suffers from can be cured," it said. "It will then be released in the sea with, we hope, better chances of survival."
Drone footage on Monday showed the white whale coming up for air as it turned slow circles in the lock just below the water's surface.
Drone footage on Monday showed the white whale coming up for air as it turned slow circles in the lock just below the water's surface.
In late May, a gravely ill orca swam dozens of miles up the Seine and died of natural causes after attempts to guide it back to sea failed.
In September 2018, a beluga whale was spotted in the River Thames near Gravesend, east of London, for a few days, in what was then the most southerly sighting of a beluga on British shores.
