The goal of beach monitoring is to determine if the beach water is safe for recreational activities and minimize the risk of recreational water illnesses. Beach goers should always remember that water conditions can change rapidly and beach monitoring results are not always representative of current water conditions. Because samples cannot be taken constantly, at best, water quality sampling can only provide a snapshot of water conditions at the time of sampling.
There are 79 public beaches along Minnesota’s coast of Lake Superior, 38 of which are monitored for bacteria. Samples are collected from Memorial Day through Labor Day.
Beaches are classified into “tiers” that determine how often they are tested.
- Tier 1 beaches are those that receive the most use by the public. These beaches are sampled at least twice each week.
- Tier 2 beaches usually receive moderate use by the public. These beaches are sampled at least once each week.
- Tier 3 beaches typically receive sporadic use, have limited access, and few potential sources of pollution in the area. These beaches are not sampled.
The quality of beach water is determined from collecting and analyzing beach water samples. Water samples are tested for the presence of an indicator organism, Escherichia coli (E. coli), because it is impractical and expensive to test for specific germs. E. coli are found in the gut of warm-blooded animals (humans, livestock, birds, pets, etc.) and are excreted in feces. Most E. coli strains will not cause illness, but their presence indicates that germs that can cause illness may also be in the water.
Beach Program staff collect water samples at Tier 1 and Tier 2 beaches by wading knee-deep into the water and taking a “grab sample” of 100 milliliters of beach water. The samples are put on ice and transported to a laboratory where they are analyzed according to US EPA approved methods. Results are typically available within 18-24 hours.
Predictive Water Quality Nowcast Models
The Minnesota Lake Superior Beach Monitoring Program has developed nowcast models that predict current water quality conditions at select Lake Superior beaches. A water quality nowcast provides information on E. coli levels similar to the way a daily weather forecast provides the likelihood of rain or sun. The nowcast models are calibrated for each beach and were developed based on historical climate and water quality measures. Models use readily available information such as rainfall, cloud cover, wave height, water clarity, and temperature to estimate the probability that E. coli counts will exceed the acceptable standard. Nowcast models allow Beach Program staff to make same-day beach advisory decisions instead of waiting until the next day for laboratory results. Beach staff use a computer program developed specifically for creating beach nowcasts called Virtual Beach.
Like with a weather forecast, there is some uncertainty with a nowcast. However, before a nowcast model is used to make beach advisory decisions it is evaluated for a number of criteria to ensure its predictions are as accurate, and in most cases more accurate, than advisory decisions made based on traditional beach monitoring protocols. These are criteria that are adhered to by all Great Lakes states that use predictive models. For more information about nowcasts models, visit the United States Environmental Protection Agency (US EPA) website: https://www.epa.gov/beach-tech/models-predicting-beach-water-quality.
A beach advisory is posted when monitoring results indicate an increased risk of getting sick from swimming or wading. Beach Program staff will post an advisory at the beach indicating swimming and wading are not recommended when any of the following instances occur:
- A single water sample exceeds an E. coli count of 235 organisms per 100 milliliters, or
- The geometric mean of E. coli counts from 5 water samples collected during a 30-day period exceeds 126 organisms per 100 milliliters, or
- Nowcast models indicate E. coli counts will exceed the single sample maximum above.
The exact cause for an advisory is often not known but could include reasons such as pollution events (such as breaks in sewage pipes or rainfall carrying pollutants into the water) or contamination of the water by bathers, pets, or wildlife. Beaches are tested daily Monday-Thursday until results indicate the advisory can be removed.