LOWELL — The flood stage level of the Merrimack River is 52 feet, and ever-so-briefly on May 11, it exceeded that threshold, recording a year-to-date high of 52.30 feet, before quickly receeding.

This map, supplied by the Friends of the Merrimack River Greenway Trail, shows the path the first phase of the project will take. Credit: Courtesy Sign up for the Concord Monitor’s morning newsletter ...