More than 400 islanders have signed an online petition against covering the St Peter Port Water Lanes.
Education, Sport & Culture want to install a metal grid over the douit in the water lanes to make the route safer for pedestrians and allow cyclists through.
The committee is motivated by the construction of a new post-16 campus nearby.
As of lunchtime on 10 July, there were 474 signatures on a petition against the changes, with commenters saying it will ruin the tranquillity of the historical lanes.
Organiser, Natalie Hughes-Davison, wants one thousand signatures.
Islanders have shared their thoughts online:
"They are old Guernsey and should be preserved as they are."
"Please preserve this little bit of Guernsey's heritage, too much has been lost already."
"I am shocked that this is even being considered and am totally against the proposal of the completely unnecessary eradication of a beautiful, tranquil and historic natural feature of our island."
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