BAR HARBOR (AP) – An earthquake Monday night could cause cloudy water in Maine wells, according to a federal hydrologist.

The quake, which occurred about 8:07 p.m. Monday, registered a magnitude of 3.9, John Ebel, director of the Weston Observatory at Boston College, said Tuesday.

An earthquake caused rocks to fall onto a road in Acadia National Park and burst some water pipes, but no injuries were reported.

The quake caused the water level in a U.S. Geological Survey well in Acadia National Park to drop more than 2 feet.

“It isn’t unusual for earthquakes to cause minor changes in water levels in wells, but this is the most memorable in Maine in the last decade,” said Gregory Stewart, a hydrologist with the U.S. Geological Survey in Augusta.

The region’s fractured bedrock makes it difficult to predict whether or not other wells will be affected. “Users of well water could notice cloudy water and possibly a change in availability of water,” Stewart said.

The quake’s magnitude was initially reported as 4.2, but Ebel said the 3.9 figure was the latest available.

It was the latest in a string of quakes to hit the region. Mount Desert Island residents experienced a magnitude 3.5 quake on Sept. 22. A magnitude 2.5 earthquake was reported four days later in the same area.

Before that, the state recorded a 3.8-magnitude earthquake in the northern part of the state on July 14.

The recent string of earthquakes follows a long period of seismic inactivity in Maine.

“We’ve been very quiet seismically since the 1990s,” Ebel said. “By contrast, the 1980s were much more active,” he said, with quakes in eastern Maine in 1984 and in western Maine four years later.

The strongest earthquake recorded in Maine occurred in 1904 in the Eastport area, according to Ebel. With a magnitude estimated at 5.7 to 5.9, it damaged chimneys and brick walls and could be felt in Massachusetts and New Hampshire, he said.