Boat owners on Waiheke Island could be fined $750 a day if they don't move their illegally moored vessels from a popular bay.

21 abatement notices - or warnings - have been issued after Auckland Council spent months trying to work out a solution in Putiki Bay.

Some still haven't been moved, clogging up the beach.

Council regulatory officer Adrian Wilson says they might even have to go to court if they still don't comply.

"To come in and ram your boat up on a beach and expect to be able to leave it up there for weeks on end, attach tyres and ropes across the beach so people can't use the beach, is not appropriate."

Wilson says some aren't even seaworthy and owners have used the beach as their private land to store their property.

He says for $750, some of them could be fixed and moved on in the next few weeks.

"It's pretty reasonable that we've given them that time to do that, but we've got to look at the whole picture. There's an awful lot of boats there that shouldn't be there."