DRBC staff preps a SPATT bag set-up to monitor algal concentrations in the Delaware River. Photo by the DRBC.

Algae are simple, plant-like organisms in aquatic ecosystems that produce food through photosynthesis, forming the base of food webs.

What are Harmful Algal Blooms (HABs)?

HABs occur when colonies of toxin-producing algae rapidly grow due to high nutrient levels, often from agricultural runoff, wastewater and/or warmer temperatures. These blooms can release toxins that can contaminate drinking water sources, becoming a public health concern. In freshwater, cyanobacteria (photosynthetic bacteria) are usually responsible for HABs. 

From a human health standpoint, as drinking water intakes are situated along the Delaware River, it is important to understand if, and where, algal cyanotoxins are detected in the river. There is anecdotal evidence that shallow water (for example, around islands) promotes algal blooms in periods of low flow and high temperature. 

Using the SPATT (Solid Phase Adsorption Toxins Tracking) methodology, the DRBC is studying the presence/absence of harmful algal blooms (HABs) toxins (anatoxin, microcystins and cylindrospermopsin) in the Delaware River.

2022 Study: August - September

  • Tidal Delaware River, 11 sites

  • Monitored using SPATT bags, collecting after eight days; a total of three rounds of this was completed

  • The Del. Dept. of Natural Resources and Environmental Control (DNREC) lab handled analysis

  • Results indicated the presence of microcystin at all sites and anatoxin-a at most sites

2023 Study: August - September

• Non-tidal Delaware River, 15 sites
  
  
• Monitored using SPATT bags, collecting after eight days; a total of three rounds of this was completed
  
  
• DNREC handed sample analysis
  
  
• Results showed the presence of microcystin in the non-tidal sites sampled

Monitoring: 2024 - 2025

• In 2024, DRBC deployed SPATT bag samplers during the autumn and winter periods to obtain cyanotoxin data outside the typical high-growth period of July through September.
  
  
• In 2025, DRBC repeated the SPATT monitoring in May through July in the tidal mainstem, with grab samples collected at deployment and retrieval of the SPATT bags.
  
  
• Samples were extracted and analyzed by DNREC to quantify the toxins adsorbed. Water column concentrations of microcystins and cylindropermopsin are being compared against the USEPA Drinking Water Health Advisories.
  
  
• Results indicate the presence of microcystins, anatoxin-a and cylindrospermopsin across all Delaware River sites.

2026 Monitoring

• In 2026, DRBC is expanding its cyanotoxin analysis to include quantitative polymerase chain reaction (qPCR), a molecular technique that amplifies and quantifies targeted genes, to identify and quantify cyanotoxin-producing genes (e.g., mcyE, cyrA, sxtA) in water samples at each site. More intensive deployments, plus the deployment of a continuous data logger, at Bristol Wharf are planned.
  
  
• The combined SPATT, grab samples, and qPCR results will provide a more robust screening framework, differentiating between toxins passing through the system (via SPATT) and those with localized production potential (via qPCR).  
  

Moving forward, DRBC plans to work with its partners to: 

• Better predict the origin and transport of cyanotoxins throughout the system 
  
  
• Identify cogeners and estimate cyanotoxin concentrations in the mainstem in all seasons