Takeaways from 2020-2021 Winter Salt Watch


Many of our Creek Watch volunteers collected Salt Watch data between late November 2020 and into April 2021.


For those unfamiliar with Winter Salt Watch, this nation-wide program is organized by the Izaak Walton League of America (IWLA) and aims to collect data on chloride levels in local streams through the power of community science and passionate volunteers! It is very easy to volunteer with the program - IWLA provides free test kits that are mailed to you when you sign up or email them. Testing a local stream is a simple process too, involving an easy-to-read test strip that is dipped into the water. The program was launched in 2018 and is growing every year! You can read more about the history of the program here.


The full extent and effects of chloride in streams is not yet well understood, and collecting a lot of data from various locations throughout the watershed is critical to understanding local trends.


This program doesn't work without the participation of volunteers like you, so thank you! In addition to collecting data, this community science program has also been incredibly valuable in raising awareness of the issue. Major news sources like the Philadelphia InquirerKYW, and local news outlets have covered the topic, getting the word out to the broader community about how salt application is connected to water quality and why it matters.

So, you might be asking, what did we find this winter from the Salt Watch data collected in the Wissahickon watershed? Below are a few results of the 2020-2021 data collection:

  • ~45% of Salt Watch readings were below 100 parts per million (ppm), which is considered the level that can naturally occur in freshwater streams

  • ~33% of Salt Watch readings were between 100 and 230 ppm, which is considered elevated above 'natural' levels of chloride

  • ~22% of salt watch readings were above 230 ppm, which is considered toxic to aquatic life over prolonged periods of time

Road salt near Willow Lake Farm in Ambler, PA

Below is a graph of all the Wissahickon data collected - this includes data from the main stem of Wissahickon and some tributaries to Wissahickon as well.

Based on the graph, you can see that the highest chloride readings (above 230 ppm) were collected throughout February, which is expected based on the series of snowstorms this region received during that time and subsequent road salt applications. Compared to last year (the data collected over 2019-2020 winter), the results of this year look much worse! Last year, ~89% of the readings collected in the Wissahickon watershed were below 100 ppm, and the remaining samples were all below the 230 ppm toxic level. However, this does not necessarily indicate a long-term trend for two reasons:

  1. the winter of 2019-2020 had less than normal levels of snow and precipitation so it was not a representative weather season and
  2. identifying trends requires data collection over a longer period of time to pinpoint what patterns are emerging over time.


Another huge change this year is that we have DOUBLED the number of volunteers collecting Salt Watch data compared with the winter of 2019-2020. This has resulted in a much more robust dataset this year, which captures more frequent measurements of chloride levels from a greater number and variety of locations and water bodies.


Based on this data the good news is that, while 22% of this winter's  salt  watch  readings exceeded the level of toxicity for aquatic life, it appears that chloride levels dropped to lower levels in all streams sampled by March. The 230 ppm toxicity level is calculated based on long-term exposure, so when chloride levels fall quickly, the risk to aquatic life is minimized. Short-term chloride exposure does not become dangerous to aquatic life until concentrations of 800 ppm or above are present - here's a good article to read more about those levels of toxicity. Thankfully, none of our readings this year were close to that level!


Interestingly, chloride in the waterways can be an issue during the summer too, although we typically collect less data then. Check out this article that explores why choride can be a concern in the summer too. We encourage you to keep collecting data and invite your friends to participate too! Please reach out to me at erin@wissahickontrails.org with any questions about the Salt Watch program.