Skaneateles’ unfiltered waiver, 130 years in: why the 2025 algal bloom did not reach your tap, and what changes for 2026

The reason a Syracuse homeowner can fill a kettle on the East Side without a treatment plant in between is a 1894 gravity pipeline, a federal filtration waiver that almost no other big-city system in the country still holds, and a chain of voluntary farm-runoff agreements signed by dairies you have never heard of in the south end of Skaneateles Lake. Last fall the system was tested in public when raw lake water at the intake pipe registered a toxin made by blue-green algae. The treated tap water did not. What happens next bloom season starts with the May 1 monitoring restart and the City of Syracuse Department of Water’s published response plan.

The lake itself is 16 miles long, on average three quarters of a mile wide, with a surface area of 13.6 square miles and a watershed of 59 square miles spanning Onondaga, Cayuga and Cortland counties. Maximum depth runs between 300 and 315 feet depending on the source, with a mean depth of 145 feet and a thermocline that sits around 35 feet down. The Town of Skaneateles maintains the south-end shoreline boundary. The City of Syracuse owns the water rights and operates the intake.

That intake feeds a 19-mile gravity pipeline first opened on June 29, 1894, when the first lake water reached Woodland Reservoir after a 4.5-day trip down the hill. A ceremonial opening on July 3, 1894 included a 100-gun salute. Skaneateles village sits 200 feet higher in elevation than downtown Syracuse, which is why the system needs no pumping to deliver roughly 40 million gallons a day to the Woodland Reservoir’s 121-million-gallon storage tank on the city’s South Side. The capacity figure has not changed materially in 130 years.

What has changed is the regulatory standing of an unfiltered surface-water supply. New York State Department of Health approves Skaneateles as one of a very small number of large-system unfiltered drinking water sources in the United States, the same category that holds New York City’s Catskill/Delaware system and Portland Oregon’s Bull Run. The federal Surface Water Treatment Rule requires filtration unless a system meets a strict watershed control plan. Cost estimates for a Syracuse filtration plant have run between $150 million and $200 million in recent reporting. There are no immediate plans to pursue construction.

The fragile piece of this story is that small body of contradictions: the lake is shallow at the ends, deep in the middle, surrounded by sloping dairy and corn ground, fed by tributary streams that the watershed plan maps in detail, and now warmer in late summer than it was a generation ago. That last fact, more than anything else, is why the September 2025 advisory happened.

On September 12, 2025, the Onondaga County Health Department issued a Blue-Green Algae Advisory for Skaneateles Lake. The trigger was confirmation by the New York State Department of Environmental Conservation of a harmful algal bloom, plus laboratory testing conducted by the City of Syracuse that detected microcystin toxins in raw, untreated lake water near the city’s intake. Microcystin is produced by certain cyanobacteria, including species in the genus Microcystis, and at high enough exposures it damages the liver. The drinking water that flowed out of taps in Syracuse did not show toxins. The raw water did.

The bloom kept growing for weeks after the initial advisory. On September 16, 2025, shoreline sampling confirmed cyanobacteria presence with blue-green chlorophyll a measured at 218.4 micrograms per liter. On September 27, 2025, a second sampling round recorded 109.35 micrograms per liter. On October 8, 2025, sampling near the Skaneateles Country Club registered 1,573.29 micrograms per liter, an order of magnitude above the earlier figures and one of the higher single-site readings any monitor has logged on the lake in recent years. DEC later confirmed the bloom dissipated as water temperatures fell.

The City of Syracuse Department of Water response is on file as standard operating practice. During HAB season, plant staff collect raw water and treated water samples and ship them to the New York State Department of Health laboratory at Wadsworth Center in Albany. Treated water is tested for microcystins and other cyanotoxins. As of the 2024 Consumer Confidence Report, no toxin had been detected in finished drinking water served to the public. The 2024 CCR is the current public document; the 2025 CCR is due to be posted to the Department of Water website by July 1, 2026 under federal rule.

The single number that explains why Syracuse still holds a filtration waiver is $21 million. That is the figure the Skaneateles Lake Watershed Agricultural Program, known as SLWAP and run through the Onondaga County Soil and Water Conservation District, has spent on whole-farm plans and best management practices since 1994. Of that $21 million, $14.7 million has come from the City of Syracuse and $6.3 million from grants. Roughly 200 farms have signed voluntary agreements over the program’s 31-year run. Practices include cover-crop planting, manure storage upgrades, riparian buffer plantings, and grassed waterways. The deal in plain English is that the City of Syracuse pays the up-front cost so the farmer is not on the hook, and the farmer agrees to a runoff-control plan that keeps phosphorus out of the lake. Phosphorus is what feeds blue-green algae.

The state has a second instrument in this story too. In June 2025, New York announced finalization of the Skaneateles Lake Water Quality Plan, the first whole-watershed plan filed for an unfiltered surface water source under New York’s revised Nine Element Plan framework. The plan identifies the highest priority sub-watersheds, sets phosphorus reduction targets, and aligns funding from the state Environmental Protection Fund with on-the-ground work. The Onondaga County Soil and Water Conservation District is the lead implementing agency.

The harder argument is between people who think monitoring is enough and people who think Syracuse should have started a filtration plant ten years ago. The first time microcystins reached the intake pipes was 2017, after a fall bloom that surprised everyone. Toxin levels were detected, treated water came back clean, the system held, and the city’s response was to spend on watershed management rather than on a treatment plant. Both 2024 and 2025 saw confirmed blooms. The pattern is that fall blooms are now part of the lake’s behavior rather than an anomaly. None has yet broken through to the finished water.

What residents on the lake should know for the 2026 season is concrete. The Onondaga County Health Department maintains a public-facing microcystin test results page that posts treated and raw water sampling outcomes through the season. The Onondaga County Soil and Water Conservation District publishes the Skaneateles Lake Watershed Agricultural Program annual report each winter. The City of Syracuse Department of Water publishes the Consumer Confidence Report each June. The DEC HABs Notification page maps every confirmed bloom in the state. The Village of Skaneateles posts a Blue Green Algae Drinking Water Information page on its municipal site for village residents who draw from the lake themselves rather than from the Syracuse system.

The cost calculus comes down to a thought experiment. Every $1 million the City of Syracuse spends on farm runoff control is $1 million it does not have to borrow toward a $150 million to $200 million filtration plant. If a future bloom shows up earlier in the season, lasts longer, or reaches concentrations that overwhelm the unfiltered treatment system, the state can revoke the filtration waiver. At that point the conversation changes from voluntary farm contracts to a sewer-style bond authorization. As of May 2026 the waiver remains intact and the Syracuse water still flows from Woodland Reservoir without a filtration plant in between.

The next public-facing milestone is the Department of Water 2025 CCR posting, due to households served by the system this summer. The Onondaga County Health Department’s microcystin testing page restarted for the 2026 season at the beginning of May. The SLWAP report should land before the new fiscal year. If a 2026 bloom shows up earlier than the September pattern of the last two years, that is the data point a resident on Lake Road or Onondaga Hill should be watching.

Update, August 6, 2026: the 2026 season is clean so far

This story asked what the 2026 bloom season would do. Two thirds of the way through it, the answer is nothing, at least on Skaneateles.

CNY Signal queried both live NYHABS layers on August 6, 2026, the archived-reports layer covering April 23 through July 23 and the current-reports layer covering July 24 through August 5. Between them they carry 569 harmful algal bloom reports from across New York State this season. The number filed for Skaneateles Lake is zero.

That is not because the region is having a quiet summer. Otisco Lake, 12 miles east, has 14 confirmed reports this season. Cross Lake has three, the Seneca River three, Jamesville Reservoir two, and Tully Lake and the Onondaga Lake Outlet one each. Onondaga County has blooms. Skaneateles, so far, does not.

Put the season in its run. State records going back to 2019 show three Skaneateles reports that year, 23 in 2020, 65 in 2021, nine in 2022, 19 in 2023, 149 in 2024 and 47 in 2025 between August 22 and September 29. The 2024 season was the worst on record by a wide margin. Every one of those seasons had its first report by early September, and 2026 has not had one at all.

The caveat a careful reader should apply: the reporting window is not closed. Skaneateles blooms have started as late as September 2 and run to October 22. Nothing in the record supports calling 2026 a clean year yet. What it supports is the narrower statement that the lake has gone through the front two thirds of the season without a confirmed bloom, in a summer when six other Onondaga County waters did not.

What the 2025 intake data actually showed

The city’s own laboratory numbers for last season are now public in the Skaneateles Lake and Watershed 2025 Annual Report, dated April 2026, and they are sharper than the advisory language suggested at the time.

Microcystin was detected in raw water at the city intakes on 17 separate dates in 2025. Sampling ran July 7 to October 22. Of 33 laboratory submissions, 26 raw samples came back at or above the 0.3 microgram per litre limit of quantitation. Broken out by intake, the toxin hit that threshold on 12 sampling events at Intake #1 and 14 at Intake #2. It was not detected at all in 2019, 2020, 2023 or 2024.

Raw water is lake water before treatment. The treated water leaving the system is the number that matters at a kitchen tap, and that stayed clean. But 17 detection dates in one season, at a supply that had four detection-free years in the preceding six, is the operational argument for why the city keeps a chlorination and monitoring program at a lake it is legally allowed not to filter.

Where the 13.4 billion gallons go

The scale of the system is worth spelling out, because the filtration waiver is not protecting a small supply. In 2024 the Department of Water drew 13,443.72 million gallons out of Skaneateles Lake, an average of 36.832 million gallons a day, and bought another 44.00 million gallons from Lake Ontario through OCWA. EPA’s Safe Drinking Water Information System lists the Syracuse system, PWSID NY3304334, as serving 192,000 people across 45,503 connections.

Now the arithmetic nobody runs. Customers were billed for 5,584.94 million gallons, 15.301 million gallons a day. The other 7,902.78 million gallons, 21.651 million gallons a day, went to firefighting, hydrant and main flushing, street sweeping, main repairs and system leaks. That is 58.6 percent of everything entering the system that never reaches a billed meter.

Per person, the system pulls about 192 gallons a day out of the lake for every resident it serves and bills about 80. A watershed protection program built on voluntary farm agreements is protecting a supply where roughly three of every five gallons drawn are lost or used before anyone pays for them.

The farm program, in current numbers

The watershed agricultural program’s own reporting, in the City of Syracuse Skaneateles Lake Watershed Program Annual Report dated April 10, 2026, is more specific than the shorthand that usually gets quoted. There are 41 operations in the watershed that meet the New York State Agriculture and Markets definition of a farm. Thirty-five are enrolled and six decline, an 85 percent participation rate, and roughly 93 percent of the watershed’s farmland is enrolled.

Whole Farm Plans are complete for 33 of them, which the program counts as 73.82 farm equivalents at 400 acres each, with implementation finished on 28 farms or 65.38 equivalents. The 2025 agricultural survey puts the worked acreage at 29,936 acres across 34 operators with active plans, down from 30,204 acres and 35 farms the year before. The program runs under a City of Syracuse contract with the Onondaga County Soil and Water Conservation District.

The regulatory backdrop has not moved since last summer. The Skaneateles Lake Watershed Nine Element Plan for Phosphorus, jointly approved by NYSDEC and the Department of State, was announced June 5, 2025. No revision or amendment has been published since. The filtration avoidance determination the city received on June 28, 2004 carries no expiration date and remains in force.