The fourth annual Maine Open Lighthouse Day will feature opportunities for the public to tour 22 coastal, island and river lighthouses.

The event, which will be held rain or shine on Sept. 15, is the largest of its kind in the country. It is being coordinated by the Coast Guard in partnership with the Maine Office of Tourism and the American Lighthouse Foundation.

The Portland Breakwater Lighthouse (Bug Light) in South Portland, Spring Point Ledge Lighthouse in South Portland and Portland Head Lighthouse in Cape Elizabeth will be among the lighthouses open for guided or self-guided tours from 9 a.m. to 3 p.m.

Some lighthouses are accessible only by boat and others may charge fees. For more information, go to: www.lighthouseday.com.