Outdoor risks through the seasons
Tick, mosquito, forest-fire, blue-green-algae, pollen and thin-ice risk in the Nordic and Baltic region — when each peaks and how to stay safe.
These are general seasonal patterns for the Nordic and Baltic region, not a live forecast. Always check the current local advisory — the weather service, health authority or water-quality notice — before you head out.
Enjoying the outdoors here means knowing what the season brings. Each risk below has its own window — ticks and pollen in spring and summer, algae and fire in the summer heat, thin ice at the turn of winter — and a few simple precautions handle most of it. Open any risk for the detail and the practical steps.
Risks to watch
Ticks (Lyme disease and TBE)
Ticks wait on grass and low vegetation in forests, meadows and gardens and attach to skin as you brush past.
Mosquitoes
Mosquitoes breed in still water and are at their fiercest around bogs, lakes and wet forest, particularly in the long northern twilight.
Forest and wildfire risk
After a run of dry days the forest floor, heath and peat dry out and ignite easily.
Blue-green algae (cyanobacteria)
In warm, still water, cyanobacteria can multiply into a bloom that looks like spilled paint, greenish streaks or a scummy film on the surface.
Pollen and hay fever
The northern pollen season is compressed and intense.
Thin ice
Ice on lakes, rivers and the sea forms and melts unevenly.
When each risk peaks
| Risk | Active season | Worst period |
|---|---|---|
| Ticks (Lyme disease and TBE) | April to October, whenever the ground is above about 5 °C | Late spring (May–June) and again in late summer (August–September) |
| Mosquitoes | May to September | Midsummer (June–August), and always worst at dusk near water |
| Forest and wildfire risk | May to August, during dry spells | Long hot, dry, windy periods in high summer |
| Blue-green algae (cyanobacteria) | July to August | Warm, calm, sunny spells on lakes and the sea |
| Pollen and hay fever | April to August | Birch in April–May, grasses in June–July, mugwort in August |
| Thin ice | The freeze of late autumn and the thaw of spring | November–December as ice forms, and March–April as it rots |
Source: Seasonal patterns follow standard public-health and safety guidance for the region; not a live forecast. · checked 2026-09-04
Frequently asked questions
When is tick season?
Ticks are active from roughly April to October whenever the ground is above about 5 °C, with peaks in late spring and again in late summer. The Baltics and parts of the Nordics are high-incidence areas for tick-borne encephalitis.
When is blue-green algae a problem?
In warm, calm water in mid to late summer (July–August). If the water is discoloured, streaky or scummy, keep people and especially dogs out of it.
Is the ice safe to walk on?
Treat early-winter and spring ice as unsafe. As a rough guide, stay off clear new ice thinner than about 10 cm, and remember snow-covered or thawing ice needs much more and can be rotten underneath.
Get outside, safely
TempoLife tracks your walks, rides and swims and helps you build an outdoor habit through the year.