Council of Canadians organizer Mark Calzavara has set up camp with allies next to Lake 468 at the Experimental Lakes Area in northern Ontario.
The Harper government has said it will close the ELA March 31.
Calzavara says, "Right now, the ELA belongs to the people of Canada. The science is done in the public interest and the data is public. We're here representing all the people who have spoken out about the potential closure of the ELA and we are not giving up."
There has been a sustained campaign by many to keep the freshwater research facility open.
Scientists have argued that it provides research critical to the protection of freshwater for the global scientific community.