No mention of a fence? Did the rabs climb a fence? Surely the reservoir is fenced. We had a similar incident at Bull Springs, Portland, OR’s water supply a couple years ago. One guy, had a camera, security cams caught him climbing the fence both ways and apparently snapping a few pics. They took his film and busted him for fence climbing.
It has 118 miles of shoreline (http://www.foquabbin.org/faxfigs.html) Cost of a fence might be as low as 10k per mile but since it's government count on 200k per mile. Border fence is a couple million a mile at the very least.