From the Boston Globe archives, May 5, 1994 (h/t Poor Conservative on twitter).
The charges against [Romney] were dropped several days later and officially dismissed in February 1982 at Natick District Court. At Romney's request, the judge also agreed to seal the records, making them unavailable for public inspection.
Romney said the guard told him not to put the boat in the water or he would be ticketed and fined $50. Frustrated and feeling that the license was still somewhat visible, Romney defied the order, saying it would be worth his while to be fined $50 to enjoy the day on the lake with his family.
When he began to put his boat in the water again, Romney said the park ranger reappeared, furious over Romney's defiance, and arrested him. Romney said he was handcuffed and taken to the Natick police station and booked.
Obviously, the Kennedy Campaign knew about it, so we must guess Obama does as well.