Tisbury Waterways Inc.’s (TWI) annual water quality test results for sites in the Lagoon, Vineyard Haven harbor, and Lake Tashmoo show varied bacterial contamination, with Cronig Avenue, the Lagoon Pond boat launch and Grove Avenue ranked as the cleanest sites. Water samples taken at Owen Little Way, Beach Road Extension, and Lake Tashmoo at Lake Avenue were among the most contaminated.
TWI reported the test results in a July newsletter. The nonprofit conducts the tests at different sites 11 times throughout the year during rainstorms, when runoff is at peak amounts, and three times when it has not rained for several days.
Runoff from rain storms can contain “nitrogen, phosphorus, animal waste, oil and heavy metals,” according to the TWI newsletter. The organization has tested Owen Little Way for the past 20 years and found at times that water quality levels were below safety guidelines for swimming set by the Environmental Protection Agency and state public health agencies.
This year’s results showed that some areas, although located quite close to one another, had dramatically different water quality levels. For example, Grove Avenue samples tested very clean and Owen Little Way samples had high levels of contamination.
TWI will continue testing throughout the summer to gather more data and to examine how far bacterial contamination may spread when it reaches the outer harbor. Increased testing after rainstorms also will be done at the end of Owen Little Way and then 100 yards to either side to determine how long bacterial contamination may remain in the water.
To combat low water quality levels at Owen Little Way, TWI is plans to create a “rain-garden” north of the Vineyard Haven Yacht Club. The garden will act as a filter to decrease runoff pollution by perhaps as much as 85 percent, according to the newsletter.