The lake at Scarborough's Peasholm Park has had to be closed due to an issue with moss.
Last week, weeds started to appear on the surface of the lake and although work to remove them started straight away, the issue could not be resolved in time for the bank holiday.
Cllr Tony Randerson said: "It was a little bit upsetting to be honest.
"In the past we've managed to get rid of these weeds with some blue dye but this time for some reason it didn't work and regrettably the only option was to close the lake.
"The council had done the right thing by dredging it a few days before the bank holiday so there's no blame on our officers. It was sods law."
The sudden growth of weeds is thought to have been caused by the cleanliness of the lake which allowed algae to spread faster.
Work is now underway to clear the moss and the lake is expected to reopen before the weekend.