Officials are trying to figure out what caused water levels to drop twice in a four-day span along the Shenandoah River's North Fork.

The Daily News-Record (http://bit.ly/NNqPAK) reports the Shenandoah Riverkeeper advocacy group has sent letters asking about 800 landowners to report unusual observations about the river.

Data taken from a U.S. Geological Survey gauge near Strasburg shows the water level dropped more than 3 inches on June 29, the day a severe windstorm struck the region. The levels dropped again on July 3.

The river's level hit 1.7 feet on June 29 after being at about 2.4 feet around June 20. In the span of a few hours on June 29, the water flow went from 175 to 65 cubic feet per second.

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