How Can An Algal Bloom Be Harmful?

We’re in the middle of our Watershed Pollution Prevention class, and the term “Harmful Algal Bloom” has come up a few times. HAB’s don’t get their own lesson, so let’s talk a bit about what they are!

What’s an HAB?

HAB’s are classified when the bloom contains visible areas of blue-green algae, or cyanobacteria. That being said, cyanobacteria can vary in color, ranging from bright green, blue/green, and brown.

Small amounts of cyanobacteria exist is healthy waterways, but can grow out of control under these conditions:

• Excess nutrients

• Warm temperatures

• Low winds

• Lots of sunlight

You might notice it has streaks or looks like spilled paint.

Is all algae bad?

Not all algae is harmful. Like we learned in the Live Food lesson, algae is an important part of the food chain (Department of Environmental Conservation). Green algae might float, bubble, look silky, or form thick rafts, but they don’t produce cyanobacteria.

How can HABs harm humans?

HABs can harm people when they come in contact with it by touching it or ingesting it. You may notice fever-like symptoms, nausea/vomiting, diarrhea, or rashes (EPA).

How can HABs harm pets and wildlife?

Harmful cells from HABs can stick to animal fur and can be ingested when the animal cleans itself. Give your pet a bath with clean water and seek veterinarian advice if your pet shows signs of distress after a potential exposure (DEC). Symptoms of HABs exposure for dogs include:

• Excessive salivation or drooling

• Disorientation or inactivity

• Elevated heart rate and difficulty breathing

HABs can also impact entire ecosystems! Think about our trout for instance. HABs deplete oxygen (which we know our trout need!) and can kill crustaceans (like our daphnia) and small fish (like our trout). What happens to our predators, like birds or larger fish, if the bottom of the food chain collapses?

How can we prevent HABs?

The general public, especially those who live on the water, can do their part to reduce the likelihood of algae blooms by reducing the addition of nutrients (phosphorus and nitrogen) to waterbodies. The amount of nutrients can be decreased by:

• Limiting lawn fertilization

• Scoop the (dog) poop

• Maintaining septic tanks

• Installing and maintaining shoreline buffers

Water Quality and Nitrogen Cycle

By now, you and your students have run tens of water quality tests. Let’s take a moment to slow down and look at what’s going on and why.

Nitrogen Cycle

Your aquarium is producing “waste”, including fish poop, uneaten food, and dead fish. The Nitrogen Cycle is the biological process that converts toxic compounds into beneficial bacteria colonies:

Waste → Ammonia (toxic) → Nitrite (toxic) → Nitrate (okay)

In the beginning, we added a weekly dose of biological enhancer (MicrobeLift Special Blend) to help these beneficial bacteria colonies form in our coldwater ecosystem.

(If we had plants in the aquarium, they would absorb these nitrates and use them as nutrients, completing the cycle. Since we don't, we can do partial water changes regularly.)

The video here might be familiar to some of you. This example by Aquarium Co-op explains the Nitrogen cycle using m&m’s. You can use this video with your students, or another one that you may prefer more. 

How To Run A Full Water Quality Test

This video features our very own Phil Koon, showing the entire process of running a full water quality test. Ideally, we’re doing this every other day to have an accurate reading of our water trends.

Recording Water Quality Data

Not only do we want to be testing our data, but we want to be recording it as well. This helps us keep an accurate record, and can show the students these biological processes in real time. You can print out and keep this Trout Care Daily/Weekly Checklist nearby your aquarium for the students to help fill out. As the teacher, you will also be uploading this information into the 2025-26 Aquarium Monitoring Data Sheet, so the DCL team has access to this information and can help you troubleshoot any issues that may occur.

Recommended Water Testing Levels:

• Ammonia- Less than 1 mg/l (ppm).

• Nitrite- Near zero (ppm), once bacteria are established in the filter system

• Nitrate- Below 40 ppm (mg/l)

• pH- The pH scale runs from 1 (acid) to 14 (basic).  7 is “neutral”.  A pH of 7.4 – 8.4 is fine for our trout

Ammonia and Nitrite at high levels are toxic to your fish. Nitrate is not, it would take up to 200 ppm for nitrate to be toxic.

What To Do if Levels are Consistently High (Over Extended Testing):

• If ammonia or nitrite levels rise above 1 ppm for an extended period, contact us.  Reducing or temporarily pausing your feeding schedule is a good first step that you can take right away.  Depending on the conditions in your aquarium, additional filter media or aquarium cleaning/gravel vacuuming can also quickly reduce these waste products.

• Nitrate levels will steadily rise during the year.  Without the presence of plants in our aquarium, the nitrogen cycle is incomplete, and there is no place for nitrate to go.  This is not a threat to your trout, but high levels will encourage algae growth, odor, etc. The only way to reduce nitrate is with partial water changes.

More Troubleshooting:

Depending on where you are consistently seeing concerningly high levels in your aquarium, you may need to troubleshoot further as to what could be the cause. A really great resource for troubleshooting is this Pennsylvania Trout in the Classroom document. It provides a great overview of the Nitrogen Cycle, and if you skip over to pages 56-58, you can find causes and remedies for high Ammonia and Nitrite levels that may help target and fix your exact issue!