Source Water Observation and Monitoring

Vulnerable Public Water Systems should begin either source water observation for algal blooms or monitoring for bloom indicators at the start of each bloom season and continue throughout the bloom season. The source observation and monitoring could potentially continue throughout the year if local climate or bloom history indicates the possibility of blooms year round. Source water observation and monitoring are described below.

A. Source Water Observation

Source water observation means regularly inspecting surface water sources for algal blooms and responding when they are found. The frequency of observation should be related to the probability of an algal bloom developing, which is often seasonal and weather dependent.

Action Result Response (follow-up testing)
Source Water Observation Bloom Confirmation Phytoplankton Identification

B. Source Water Monitoring

In addition to observation, a Public Water System may choose to regularly monitor source water for bloom indicators. Bloom indicators have the benefit of detecting HABs and cyanobacteria that may not be visible but may be producing cyanotoxins. Here is a summary of possible HAB or cyanobacteria indicators that could be sampled throughout the bloom season and levels that would trigger a response:

Alert Level 1 Thresholds

Bloom Indicator Trigger Level Response (follow-up testing)
Secchi disk depth Reduction of >2 ft in visibility since prior measurement Additional Bloom Indicator testing
Lake Turnover Lake Turnover (temperature and DO levels indicate lake is not stratified) Additional Bloom Indicator testing
MIB &/or Geosmin Increase of 1-2 ppb (depends on utility goal) Cyanotoxin testing
Phytoplankton Cell Counts ≥ ? cells/mL Cyanobacteria Identification
Cyanobacteria Cell Counts ≥ 2,000 cells/mL* Cyanobacteria Identification
Bio-volumes ≥ 0.2 mm3/L* Cyanobacteria Identification
Chlorophyll-a ≥ 1 µg/L* Cyanobacteria Identification
Phycocyanin equivalents ≥ 2,000 cells/mL Cyanobacteria Identification
Cyanotoxin Production Genes ≥ ? Cyanobacteria Identification

*(WHO, 6.3.2, 1999) “Alert Level 1 Thresholds”

The recommended cyanobacteria identification test enables a water system to focus on cyanotoxins typically produced by a group of cyanobacteria and to establish which to test for in raw or finished water. Appendix B provides a table of cyanobacteria and their associated cyanotoxins.

It may also prove useful to communicate with nearby/upstream systems (e.g., blooms in source water or cyanotoxin occurrence in their raw water) and determine potential water source similarities that would facilitate similar operational actions.