WEBSTER, N.H. (AP) – A 40-year-old construction flaw is responsible for a leak in the Pillsbury Lake dam, state and water district engineers say.

The lake was drained for the second time in less than two years after water district officials discovered a significant leak in July. The lake had just been refilled in May, following a year of repairs needed after floods a year earlier.

The water district has about $150,000 left from making the repairs, enough to cover the cost of fixing the new leak, said District Commissioner David Klumb.

Steve Doyon, a regulator with the state Dam Safety Bureau, said the leak was caused partly by poor construction when the dam was built in 1965 and partly by recent repairs to other parts of the dam.

Doyon said contractors created a temporary bypass and later used dirt and rocks, not concrete, to fill it in.