Restoring Lake Warner requires good science and a clear understanding of what different treatment options actually do. Friends of Lake Warner appreciates community members raising questions about the use of Phoslock and the long-term health of the lake. We take these concerns seriously and rely on independent scientific research, regulatory review, and real world monitoring data to guide our understanding.
Why phosphorus reduction matters
Excess phosphorus is the root cause of Lake Warner’s recurring harmful algal blooms. It drives oxygen loss, stresses fish populations, and suppresses native aquatic plants. Over decades, large amounts of phosphorus have accumulated in the lake’s sediments. Even if all watershed inputs stopped tomorrow, this “internal loading” would continue to feed algae for decades.
Phoslock offers a way to interrupt this cycle. When applied, it binds free phosphorus in the water and sediment, forming a stable mineral that locks the nutrient out of circulation. This supports clearer water, improved fish habitat, stronger biodiversity, and a more balanced, self-sustaining lake system.
Lower impact than other options
It’s important to consider the alternatives. The main options besides Phoslock — dredging or older aluminum-based chemical treatments — come with far greater cost and far more environmental disturbance. Dredging requires heavy machinery, destroys habitat, and can release buried contaminants. Older chemical treatments often require repeated applications and temporary water use restrictions.
Compared with these approaches, Phoslock is targeted, minimally disruptive, and significantly more cost effective. This means achieving meaningful water quality improvement with far less ecological impact and far lower expense.
Lanthanum in Phoslock
Some concerns raised in a recent letter to the editor involve the presence of lanthanum, a naturally occurring rare earth element that makes up about 5% of Phoslock. It’s important to clarify that in Phoslock, lanthanum is not present as a free metal. It is bound to a bentonite clay matrix and, once in the water, rapidly binds with phosphorus to form an insoluble mineral. This form of lanthanum is not biologically available in the way that soluble lanthanum salts are in laboratory toxicity studies.
To further ensure safe use, the proposed CPA funded 2026 phosphorus evaluation will provide the data needed to precisely calibrate the Phoslock dose for Lake Warner. Using site specific measurements and licensed applicators, Friends of Lake Warner can apply only the minimum amount needed to bind available phosphorus, thereby minimizing the amount of lanthanum introduced to the lake.
Bioaccumulation and aquatic life
Laboratory studies showing lanthanum accumulation typically use soluble lanthanum at concentrations far higher than anything found after Phoslock applications. Field studies across many lakes consistently show:
• Very low lanthanum levels in the water column
• Lanthanum remains bound in sediments and does not biomagnify
• No consistent evidence of toxicity or reproductive harm to fish, turtles, snails, or invertebrates
• Regulatory agencies in multiple states and countries classify Phoslock as low risk when used properly
Real world data simply do not support the claim that Phoslock poses meaningful risk to wildlife.
Clarifying the “nuclear waste” misconception
The letter to the editor also suggested that the lanthanum phosphate mineral formed by Phoslock, rhabdophane, is “radioactive.” This is incorrect. Natural lanthanum is overwhelmingly composed of a stable, non-radioactive isotope, and the trace isotope present is so weak that its radioactivity is negligible.
Rhabdophane is mentioned in connection with nuclear waste not because it is radioactive, but because it is used to contain harmful materials. At cleanup sites, rhabdophane binds contaminants so they cannot move or spread. In Lake Warner, it does the same stabilizing work — only with phosphorus, a nutrient that harms the lake when left mobile.
Watershed factors still matter
While the in lake treatment is the priority of the current three-year plan, watershed inputs remain an ongoing challenge. Urban stormwater and agricultural runoff continue to deliver phosphorus at levels above what the ecosystem can sustain. Long-term health for Lake Warner requires addressing both internal loading and reducing external nutrient sources through better stormwater management, riparian buffers, and agricultural best practices.
Our commitment
Friends of Lake Warner is committed to transparent communication and evidence-based stewardship. We will continue to monitor scientific findings and regulatory guidance to ensure any restoration steps prioritize the health of the lake, its wildlife, and the broader community that cares for it.
Brian Pearson is president of the Friends of Lake Warner & the Mill River. He lives in Amherst.