A hot afternoon, the swimming lake looks inviting at first glance, but there are greenish streaks on the shore. This is exactly when families should not just go into the water. Behind such discolorations can be blue-green algae, technically cyanobacteria. Not every green spot is automatically dangerous, but warning signs should be taken seriously.
Caution is especially advisable with children because they swallow water more easily while playing and stay in the shore area for longer. Anyone who takes a quick look before swimming, checks official notices, and avoids the water in case of doubt saves themselves unnecessary risks.
What are blue-green algae?
Blue-green algae are not classic algae, but bacteria that can occur in stagnant or slowly flowing bodies of water. In warm weather, with plenty of light and suitable nutrients, they can multiply rapidly. This sometimes creates greenish carpets, streaks, or cloudy water areas.
The problem is not just the appearance. Some cyanobacteria can produce substances that can irritate the skin, gastrointestinal tract, or mucous membranes. Therefore, the rule is: If the water looks suspicious or there is a warning, it is better not to swim.
Warning signs at the lake
- Greenish streaks: Especially on the shore or in sheltered bays.
- Cloudy, "pea soup-like" water: If your own feet are barely visible in shallow water, caution is advised.
- Deposits or flakes: Do not ignore floating carpets, foam, or green accumulations.
- Unpleasant odor: A musty or putrid smell is an additional indication.
- Warning signs: Local warnings take precedence over your own impression.
Important: Blue-green algae can shift due to wind. A lake can appear unremarkable in one spot and look significantly contaminated in another.
Check briefly before swimming
First, look at the official bathing water information and notices directly at the swimming lake. Many federal states and municipalities publish current readings or warnings. For larger bathing areas, it is also worth taking a look at notices on site.
If you are unsure, the simple family rule applies: Do not go in, do not let anyone swallow water, and do not let children play in the suspicious shore area. Another swimming spot, an outdoor pool, or a later visit is the better decision.
After contact with suspicious water
If children or adults have accidentally been in suspicious water, they should shower thoroughly, change wet swimwear, and monitor their skin and eyes. If nausea, vomiting, diarrhea, skin irritation, fever, difficulty breathing, or unusual fatigue occur after swimming, medical advice should be sought.
Dogs should also be kept out of suspicious water. They drink lake water more easily and lick their fur after swimming.
What belongs in the beach bag
- Drinking water: So that children do not put lake water in their mouths for fun.
- Towel and change of clothes: In case you prefer to change locations after a quick check.
- Wet wipes or water for rinsing: For hands and feet if there is no shower nearby.
- Sun and heat protection: Even if the swimming stop is shorter, shade, headgear, and drinking remain important.
The best decision is often unspectacular
Blue-green algae do not need to be dramatized. However, they are a good reason to plan swimming days consciously. Anyone who checks official information, looks at the water and shore, and takes warning signs seriously usually makes the right decision quickly. In the case of visible streaks or warnings, it is not a lost swimming day, but simply a sensible change of plan.
Read also
- Swimming after heavy rain: When families should rather wait
- Swimming lake with children: safely through hot outdoor pool and lake days
- Travel medicine cabinet in summer: What families should pack
- Too much sun: What makes sense after a day at the lake, in the garden, or on the balcony
- Beach bag after the outdoor pool or lake: What needs to come out immediately
Sources and further information
- AGES: Bathing water monitoring
- Gesundheit.gv.at: Bathing water quality
- Ministry of Social Affairs: Bathing waters
- City of Vienna: Bathing water quality and examinations
Article image: AI-generated symbolic image.
