PORTLAND – Maine wardens will monitor lakes and ponds over the holiday weekend to enforce a new sticker program that aims to educate boaters about invasive aquatic plants.

Powerboats are required to display the stickers, which cost $10 for residents and $20 for out-of-state boaters.

The fees pay for an information campaign to help keep Maine free from invasive plants, particularly Eurasian milfoil, which can quickly choke up fishing, boating and swimming spots.

“Money provided by the sale of these stickers has allowed the increase of patrols around the state and has allowed us to increase our printing of educational materials,” said Mark Latti, spokesman for the Maine Warden Service.

The trick for boaters – especially those from outside of Maine – may be finding a sticker over the holiday weekend.

Boats without stickers faces fines of up to $150. Boats carrying fragments of Eurasian milfoil face fines of up to $5,000.

Boats that carry small fragments of milfoil can spread the plant to other parts of a lake and other bodies of water.

Jim Ahearn of Shapleigh said friends from Massachusetts decided against bringing their boat to his camp at Square Pond because he was unable to get them a sticker.

“I’ve been two places nearby, but they didn’t have any stickers,” Ahearn said.

Boonie’s Country Store in Shapleigh had only two resident stickers left before the holiday. The Acton Trading Post was all out of nonresident stickers.

The Shapleigh Town Hall had several dozen left, but won’t be open again until Tuesday.

“Quite a few people from out of state have come in this week,” said town clerk Jennifer Roux. “Some people just get them with the registration and others ask for them specifically.”

Claire Morrison, clerk at the Sanford town office, said there were no more nonresident stickers, but that more were expected by Friday.

Latti suggested that boaters try Wal-Mart and Rite Aid stores.