A program to be held at the Vineyard Haven Library on Wednesday, May 4, beginning at 7 pm, is a presentation of Tisbury Waterways, Inc. The illustrated lecture will detail the installation of its bio-swale at the base of Owen Little Way in Vineyard Haven. Bio-swales, or vegetative buffers, are a natural landscaping way to filter stormwater run-off to prevent pollution of marine environments. Learn why bio-swales are key pollution fighters in commercial settings or in your own backyard, and how you can “grow” your own rain garden. If you recently heard Dori Smith speak to the Garden Club of the Back Bay on the subject of rain gardens, this program will interest you.