An Advancing Salt Front is Impacting Our Drinking Water

​By Paul Malmrose, Hudson 7 Technical Advisor/Engineering
(Click on image above to watch the presentation from 2022)

While climate change and rising sea levels have drawn widespread attention to flooding, another serious and less visible threat is already unfolding.  The salt front is moving farther up estuaries such as the Hudson River. The salt front’s position varies throughout the year, based primarily on the amount of freshwater flowing into the Hudson from upstream and its various tributaries. As sea level rises, the salt front’s position remains variable, but saline water from the ocean effectively pushes farther inland more frequently. Already, during certain drought conditions, water treatment plants issue advisories to alert those on low-sodium diets that their water contains elevated sodium levels, and these episodes often correspond with an increase in complaints about the changing taste of tap water. If salinity levels persist at high concentrations, drinking water may become unsafe or unpalatable unless alternative sources are secured or treatment is implemented–potentially at an astronomical cost.

Since 1900, sea level in the lower Hudson has risen 15 inches.  Sea level along the tidal Hudson is projected to increase by 12 to 17 inches by the 2050s and by 25 to 46 inches by the 2100s compared to a 1995-2014 baseline.  While sea-level rise is increasing, salt intrusion is influenced by multiple factors that make predicting future conditions difficult. For instance, past sea-level rise has not resulted in a notable consistent change in salinity in the mid-Hudson in part because there have also been increases in precipitation and freshwater runoff, which help prevent saline water from pushing farther north. The Hudson River Drinking Water Intermunicipal Council (Hudson 7) – a partnership of seven municipalities and two counties–came together to address emerging threats such as the advancing salt front. Hudson 7 includes the City of Poughkeepsie, the Village of Rhinebeck, the Towns of Poughkeepsie, Hyde Park, Rhinebeck, Esopus and Lloyd, as well as Dutchess and Ulster Counties, collectively serving more than 107,000 people. 

In February 2021, Hudson 7 contacted the New York State Department of Environmental Conservation (DEC) to ask whether any studies had been conducted to determine the effects of sea-level rise on the salt front in the Hudson River. DEC had recognized on its website that the salt front could extend further north in the Hudson River, though much of the public discussion had focused on flooding.  DEC also noted that the United States Geological Survey (USGS) had been collecting data on salt concentrations in the Hudson River, and agreed that a study to better understand the issue would be valuable.  

In January 2022, Hudson 7 contacted environmental experts from Riverkeeper, scientists from the Cary Institute, engineering experts from Tighe & Bond and Jacob Engineering Group, scientists from USGS, professors from Cornell and Marist University, as well as regulators from DEC, the Department of Health (DOH), and drinking water operators from the Hudson Valley.

In February 2022, Hudson 7 organized a meeting with these experts to share information about the advancing salt front. The salt front is defined as the point where chloride concentrations reach 100 mg/L–far below seawater’s 19,000 mg/L. Under both federal and state drinking water standards, chloride limits are classified as a Secondary Maximum Contaminant Level, which relates to drinking water aesthetics such as taste, odor, and color.  Chloride concentrations must remain below 250 mg/L, in order to avoid a salty taste. There are no regulatory limits for sodium, but federal and state health guidelines recommend that sodium concentrations remain below 20 mg/L for individuals on very low-sodium diets, and below 270 mg/L for those on moderately restricted-sodium diets. 

Currently, the City and Town of Poughkeepsie’s water consistently exceeds the 20 mg/L sodium threshold, averaging around 25 mg/L in recent years, with a gradual increase in the annual average over time. During the salt front event of 2025, some high tides had sodium concentration levels that exceeded the 270 mg/L sodium guideline for moderately restricted diets, and chloride concentrations were above the 250 mg/L Secondary Maximum Contaminant Level (SMCL).  The 2025 salt front event brought the highest chloride concentration on record for the Poughkeepsies’ Water Treatment Facility (PWTF) at 1,100 mg/L. This is more than three times higher than the recorded chloride concentration of 342 mg/L that occurred during the 1960s drought when the salt front advanced as far north as Kingston. 

Sea-level rise is expected to worsen the problem. These increases could push the salt front farther up the Hudson, potentially affecting all five drinking water treatment plants in the Hudson Valley. Similar concerns have been raised along the Delaware and Savannah Rivers.

In February 2022, Hudson 7 and Riverkeeper submitted written testimony to the New York Joint Legislative Public Hearing on the Executive Budget Proposal for Environmental Conservation, requesting funding to study salt front advancement. As a result, $500,000 was awarded to the USGS to develop a probabilistic model to predict salt front movement. 

At the same time, Hudson 7 organized a series of meetings to define studies and action plans, including:
  

1. Probabilistic Model for Salt Front Prediction – Projecting the location of the salt front and the number of days it may affect drinking water intakes and ecosystems over the next 50 years. 
2. Engineering Study to Develop Solutions for the Advancing Salt Front:  Evaluating potential responses, such as alternative water sources or additional treatment, both of which could be extremely costly. 
3. Ecological Effects of the Advancing Salt: Assessing impacts on Submerged Aquatic Vegetation (SAV), wetlands, and aquatic life. 
   
   

These study scopes were finalized at the Hudson 7 meeting on September 28, 2022, and submitted to DEC.  Following this work, on October 24, 2024, DEC held a kickoff meeting with USGS. The project is now scheduled for completion in September 2027.  This spring, DEC and USGS plan to meet with Hudson 7 and other experts to review scenarios. Additional information is available on the USGS website.

​While the probabilistic model is underway, it represents only the first step. If the model indicates that drinking water will be at risk, communities and water providers can begin the hard work of developing and funding solutions. The model might not show an immediate threat, but sea level rise is almost certain, and increased freshwater flows from precipitation, as well as the river’s geomorphology, are additional factors that will influence salt front conditions. 

The urgency of this issue became unmistakable this past summer when drought conditions reduced river flow, and Atlantic storms pushed salt water farther upriver. As a result, the City of Poughkeepsie had to notify customers on very low-sodium diets to avoid drinking tap water.

As this history shows, Hudson 7 has been addressing the advancing salt front since February 2021–nearly five years ago. With DEC’s first phase of the study expected in September 2027, staying informed about local water conditions is key to protecting drinking water in the years ahead.  

For more on this, read: Hudson 7: Seven Campaigns and Key Actions 2020-2024 (The Advancement of the Salt Front in the Hudson River Due to Climate Change)