Hmmm, I was surprised why the OP would drive 2 hrs and pay tolls to get to Plum Island. Just take rte 28 between Alton and Wolfeboro to Robert's Cove Rd, down to the marina. Plum Island is right out in the Cove. Nice little island, home to a floating loon nest that plays host to a nesting pair every year.
Ok, there's the lake connection.
Dave