Industrial mercury contamination in the Penobscot River has moved up the neighboring Orland River, held back by just a nearly century-old dam that needs expensive repairs or replacement.
The tide now regularly washes over the top of the dam from the mercury-contaminated water below, potentially carrying some of it upstream. Mercury has been found in smaller amounts above the dam.
The town of Orland is investigating options to fix up or replace the dam and hold back waters during even extreme tides. It also wants to improve the attached fishway, a key to maintaining — and ideally increasing — the town’s commercial alewife harvest.
The dam has to stay in place to contain the mercury, and fishway options are also limited to avoid disturbing it. Work is expected to cost millions and depend on outside funding. The situation shows another way that mercury discharged in the neighboring river decades ago continues affecting neighboring communities and ecosystems as a major cleanup on the Penobscot takes early steps this summer.
The village dam was built in 1930 to supply papermaking at the mill in neighboring Bucksport, but never used for that purpose. Residents voted to take ownership of the structure from Verso in 2010, and six years later voted not to remove it; keeping it in place also avoids changing the landscape and problems with a road bridge not meant to withstand tides.
The tide consistently rises over the dam, not just during extreme storms. Pete Robshaw, the town’s longtime fish warden, has observed that water covers the dam about once a month, around the full moon, when the tides are strongest.
The mercury on the downstream side came from the former HoltraChem factory in Orrington, up the Penobscot River, in the late 1960s and early ‘70s. The Orland River branches off of the Penobscot.
A 2022 court settlement over the contamination created a trust for remediation projects in neighboring towns, which funded $310,000 for Orland’s investigation of dam and fishway work.
Orland is one of a few Maine towns that has kept a commercial alewife harvest for decades, though harvests have increased elsewhere in recent years as dams are removed and fish passages improved.
The town brought in between 1,355 and 2,960 bushels between 2020 and 2024, earning it around $10,000 or more, according to Robshaw. Alewives are used as lobster bait and also fill a key role in the food chain, feeding other fish and birds.
They return from the sea each spring to head upriver and spawn. Village fishway improvements would benefit them primarily, but elvers are also harvested in the river, and Robshaw sees occasional brown trout and bass.
The dam gates he manually opens and closes to maintain water levels are in bad shape, Robshaw said, and would benefit from an electric or hydraulic replacement. Wooden planks on part of the spillway are eroded, and young alewives drop into them and get stuck.
A previous wooden fishway parallel to the spillway worked well until the 1990s, when the mill’s owners replaced it with a cheap structure that doesn’t work as well, in his view. He would like to see a wooden structure returned.
Engineers from Verdantas have collected data on the dam and fishway and identified several options for work on both that they’ll narrow down in the coming months. The Downeast Salmon Federation is its project manager.
An engineer’s inspection of the dam in April revealed no immediate issues, but found it was in fair to poor condition, particularly around the concrete gate area. It could be reinforced with options like a concrete cap with sheet piles or replaced with a new concrete structure, engineer Gary Allen of Verdantas said at a Wednesday presentation.
Options to limit the overtopping and prepare for extreme high tides include adding a hinged flashboard that could be raised and lowered, a gate on the crest of the spillway or an inflatable rubber dam.
Those are typically used for rivers with flow coming from one direction, not both like in a tidal river, Allen noted.
Fishway improvements would aim to let fish make it upstream for most of the tide cycle, not just during a small part as it currently does.
The initial fish ladder options are a “vertical slot,” or concrete channel that creates a kind of ramp; a “denil” ladder with a series of baffles along the sides; or a pool and weir design, which has pools separated by low barriers.
Dam rehabilitation and fish passage improvements might run $5 million to $15 million, while dam replacement with fishway work could cost $20 million.
A feasibility study should finish in September and defined options with cost estimates are expected by the end of October, Allen said.
The town would seek outside funding for such a project, Robshaw said, though he’s not sure how easy it will be to come by money to keep a dam rather than remove it.
