The Middlesex Canal Association will host a talk by Robert Thorson, the author of The Boatman: Henry David Thoreau’s River Years. His 2018 talk on Thoreau’s river years is on video in the Internet Archive. His October 27 talk will be about the river, the Billerica dam and Thoreau, timely as the US National Oceanic and Atmospheric Administration wants to remove the dam as a barrier to some fish species. Dr. Thorson is a professor of geology at the University of Connecticut.