Why is Blue-Green Algae a Problem?
Summer has only just begun, and we are already seeing reports in the UK and the US about blue-green algae blooms. It's one of the few things a portable water purifier CAN'T protect you against when wild swimming or camping, so you need to be able to recognise it.
Blue-green algae is actually not algae at all—it's a type of bacteria called cyanobacteria. Under the right conditions, cyanobacteria can multiply rapidly and form large blooms on lakes, rivers, reservoirs, canals, and ponds.
What causes blue-green algae blooms?
Blooms are most likely when several factors come together:
- Warm temperatures (typically during summer and early autumn)
- Still or very slow-moving water
- Sunlight
- High levels of nutrients, particularly:
- Phosphorus (from fertilisers, sewage, detergents, animal waste)
- Nitrogen (from agricultural runoff and wastewater)
- Low water turnover allows the bacteria to accumulate
Climate change is increasing the frequency and duration of blooms in many regions because warmer temperatures favour cyanobacteria growth.
Why is blue-green algae dangerous?
Some cyanobacteria produce toxins that can affect people, pets, livestock, and wildlife. A water purifier will remove cyanobacteria, but not the toxins they produce.
Risks to humans
Exposure can occur through:
- Swimming or water sports
- Accidentally swallowing contaminated water
- Breathing in water droplets or spray
Symptoms can include:
- Skin rashes and irritation
- Eye irritation
- Stomach cramps, nausea, vomiting, and diarrhoea
- Headaches and fever
- In rare cases, liver or nervous system damage
Risks to dogs and animals
It's not just humans that are affected by the toxins; dogs are particularly vulnerable because they:
- Swim in contaminated water
- Drink from lakes and ponds
- Lick algae from their fur
Symptoms can develop very quickly and may include:
- Vomiting
- Weakness
- Seizures
- Difficulty breathing
- Liver failure
Some cases can be fatal within hours.
Environmental impacts
Blooms can also:
- Block sunlight from reaching aquatic plants
- Reduce oxygen levels when they die and decompose
- Kill fish
- Harm aquatic ecosystems
How can you identify blue-green algae?
Common signs include:
Visual appearance
- Bright green, blue-green, turquoise, brown, or reddish water
- Surface scums that resemble:
- Spilled paint
- Pea soup
- Green paint flakes
- Thick green mats
- Clumps gathering along shorelines where the wind pushes them
Water appearance
- Cloudy or discoloured water
- Green streaks or swirls beneath the surface
Smell
Some blooms produce earthy, musty, grassy, or septic-like odours.
A simple field test
While not definitive, grab a stick and poke it:
- Duckweed consists of tiny floating leaves with visible roots.
- Algal blooms tend to form streaks, scums, or paint-like films without distinct leaves.
However, you cannot tell whether a bloom is toxic just by looking at it, and even a small bloom may contain dangerous toxins.
Safety advice
If you see water that looks suspicious:
- Stay out of the water
- Keep children and pets away
- Do not drink water from the source - even if you have a purifier
- Avoid fishing or collecting water from the affected area
If you're unsure, it's safest to treat any blue-green algal bloom as potentially toxic until local authorities confirm otherwise. Blooms are often reported, so before you travel, check the local news and environmental agencies. Don't assume that no report means no blue-green algae; stay vigilant.
At LifeSaver, we always recommend you do your research on where you are going and choose the cleanest-looking water you can find, ideally, running water rather than lakes and ponds. Water that looks muddy or dirty will clog your filter and shorten its useful life far more quickly than running clear water through it. Never forget that clear water will still carry microscopic bacteria, viruses and protozoa (parasites).
If you'd like to learn more about water that can't be treated using a water purifier, check out our blog 'Can my lifesaver filter pee?' Alternatively, you can get in touch with us.
