4  Conclusion

In 2024, cyanobacteria levels in the Charles River varied significantly, with 34% of days classified as low risk, 27% as medium risk, and 39% as high risk. Late summer saw notable harmful algal blooms, making 2024 an outlier compared to previous years, which recorded no high-risk days and higher percentages of low-risk days (71% in 2021, 54% in 2022, and 82% in 2023). On average, safe-for-swim days in the Charles River may be closer to 60% of the May-October season.

Rainfall showed no significant correlation with cyanobacteria levels. However, rainfall’s potential role in fecal contamination highlights the need for monitoring fecal bacteria like Enterococci. Expanding the monitoring system to include fecal bacteria is crucial for more comprehensive swim safety advisories.

Future efforts should also prioritize qualitative research to understand how local swimmers perceive the river’s water quality and the barriers to its recreational use. Additionally, analyzing a broader historical dataset of cyanobacteria and rainfall would help uncover long-term patterns and improve predictive models for harmful algal blooms. Together, these initiatives will enhance our understanding of how environmental and microbial factors interact, ultimately improving water quality management and public health outcomes in urban waterways.

4.1 Future Work

  1. Incorporate Fecal Bacteria Monitoring. To enhance the assessment of water safety, it is crucial to collect fecal bacteria data, either through remote sensors or manual sampling. Fecal contamination is commonly monitored using enterococci, an EPA-approved indicator of disease-causing microorganisms such as bacteria, viruses, and protozoa. Including fecal bacteria in the analysis would provide a more comprehensive picture of water quality, especially following rainfall events when contamination levels may spike.
  2. Conduct Qualitative Research on Swimmer Perceptions. Understanding the perceptions of local swimmers can offer valuable insights into the barriers to river recreation and public health concerns. A qualitative survey of urban swimmers in Boston should address key questions such as:
    • How do swimmers perceive the quality of water in the Charles River?
    • What are the main deterrents that prevent swimmers from using the river for recreation?
  3. Investigate More Historical Cyanobacteria Data and Correlations with Rainfall. Expanding the analysis to include more historical years of cyanobacteria data could help identify long-term trends and patterns in harmful algal bloom (HAB) occurrences. The expanded dataset would improve the predictive power of models and provide deeper insights into how rainfall influences water quality over time.

4.2 References and Further Reading

  1. Sensor-based detection of algal blooms for public health advisories and long-term monitoring
  2. Charles River Conservancy Swim Park Project / Urban River Swimming: Six American Initiatives
  3. EPA Charles River Buoy Information
  4. River Keeper Testing Methodology
  5. Hudson River Estuary Data
  6. Save The Boston Harbor Report Card
  7. Charles River Watershed Association Water Quality Data
  8. CDC Harmful Algal Blooms