05/05/2026
UPDATED 5/15/26
We've gotten a lot of questions about what happend to the "pond" at the Beaver Brook North Reservation. Here is a history of the pond and what happened courtesy of WLT board member and Waltham historical maven Marie Daly! Since the original post, WLT has learned a bit more about the pond's origins so we've made a few minor corrections and updates on current conditions as of this week.
The wetlands at the southeast corner of the former Metropolitan State Hospital, now Beaver Brook North Reservation, had been recently transformed into and pond about 9 years ago. The pond suddenly drained in December 2025. The area had been a wetland, called “Five Pound Swamp” in early deeds, since at least the seventeenth century and probably for thousands of years. The wetlands at the former Met State are protected by a state natural resources act in the 1970s (see map). Several spring-fed streams coming off the surrounding hills drain into the low-lying area. When the Metropolitan State Hospital was built in 1930, a culvert was built under the dirt road. The culvert connected two wetlands, which ultimately drain to Beaver Brook and the Charles River. The culvert failed about nine years ago, causing the wetlands to periodically flood the dirt road. A couple of years later, the DCR installed drainage pipes to funnel the floodwaters across the dirt road. The higher drainage pipes resulted in a pond formation. Some observers, including the DCR have theorized that the original culvert blockage suddenly cleared and the pond drained. The pond may now revert to its original wetlands state.
To complicate matters even further, there is a sewer drain in the dirt road right by the wetlands culvert. After heavy rains back in the 1990s, the drain would overflow with raw sewage. So there is a possibility that the pond water has drained into the sewer.
Also in the 1990s, the MWRA was planning to put a sludge (sewage) processing plant and sludge dump in these wetlands. They assured city officials and the public that odors and flies would be minimized. But they dropped the plan when a map of the state-protected wetlands was brought to their attention. The sludge processing plant was instead built in Quincy. Since then, the plant has exploded or caught on fire at least three times. One more reason why advocating for the preservation of our open spaces is so important!
Updates: Once the water drained from the marsh, a mud flat formed, drawing a variety of shorebirds. As of May 2026, the drain that suddenly opened in December 2025 seems to have gotten clogged again; the water level in the marsh/mud flat is rising. Hikers in Beaver Brook North Reservation have noticed that the portion of the Western Greenway that bisects a marshy area has been flooded for some time. Some have speculated that the pond draining has caused this flooding, but that is not the case, as the water is flowing across the trail from the north. Beavers have constructed multiple dams on Beaver Brook, causing the brook to overflow its banks and flow through Beaver Brook North Reservation, rejoining the brook further downstream. DCR has been informed; the next steps are up to them.
