A study revealed that the green algae bloom in the Rauma Canal was caused by Euglenid algae
Uutinen
A continuous sheet of green algae rising to the water’s surface appeared in the Rauma Canal in late summer. Smaller and shorter-lived occurrences of this kind have been observed annually. Because the bloom lasted longer than usual and covered a wide area, the City’s Environmental Protection Department took a water sample from the Canal at the end of August and had it analyzed in a laboratory.
According to the study, the algae mat consists of the euglena species Euglena granulata. There was only a small amount of blue-green algae in the sample.
– It’s fairly common for small bodies of water to suffer temporary over-enrichment problems after dredging, because the newly exposed bottom releases excess nutrients into the water, which can increase algae growth. This effect diminishes over time, says environmental protection inspector Joakim Sjöroos.
The Canal was dredged in two phases during the summers of 2024 and 2025, from the Wänni Bridge to the Vähämaanpuisto Bridge.
– In the upper sections, there were no algae blooms. These areas have more bottom vegetation, which has likely bound the nutrients to itself, Sjöroos continues.
Euglenid algae blooms can be harmful to health, but since there are no swimming areas or other significant water use in the Canal, no health risks are expected. However, it is still recommended to avoid contact with the water during the blooming period.
