Rowers on Italy’s River Po near Turin are contending with extensive algae blooms fueled by a combination of prolonged heatwaves and agricultural runoff. The blooms, which have been developing since May, have transformed parts of the river into dense mats of green vegetation, complicating navigation and altering the river’s ecosystem.

The River Po, Italy’s longest waterway, is experiencing a marked reduction in water flow, currently at about half its usual level for this time of the year. This decline is attributed to below-average rainfall and sustained high temperatures throughout June and July. These conditions, aggravated by climate change, have created a hospitable environment for algae to proliferate. Local rowing coach Roberto Romanini described the situation, noting how the thick vegetation clings to oars and impedes boats attempting to move through it.

Authorities and environmental experts have reported a mixture of algae species present, including native Spirogyra—commonly known as mermaid’s tresses—alongside the invasive Blitum nuttallianum, or Nuttall’s povertyweed, which originates from North America. The algae growth has been observed trapping debris at a 19th-century dyke and providing new habitats for wildlife such as heron chicks near the historic Isabella Bridge.

Francesco Tresso, deputy mayor of Turin, characterized this year’s algae buildup as “quite exceptional,” citing the river’s transformation into what resembles a warm lake, with temperatures rising up to 28 degrees Celsius. The rapid plant growth is linked to nutrient runoff, particularly from livestock farms throughout the river basin, which enriches the water and encourages blooms.

Environmental advocate Alice de Marco, from the organization Legambiente, emphasized that the key driver behind the algae’s spread is the excessive nutrient load from agricultural activities. She suggested that curbing or eliminating pesticide use in farming would be an important step in addressing the problem. De Marco also pointed out that algae blooms disrupt the aquatic food chain by depleting oxygen levels, which harms fish and other organisms.

Algae invasions have not been confined to the Po. Similar outbreaks have been reported this summer in Lake Iseo in Lombardy, as well as in waterways in France and Spain’s Ebro River. In Turin, city officials are actively working to remove the thick algae mats as part of efforts to revitalize the river and make it an urban attraction. Excavators on barges extract the vegetation, which is then collected by trucks daily and converted into compost. To date, over 150 tons have been removed, at an estimated cost of around 100,000 euros ($115,000).

Secondo Barbero, director of the Piedmont Environmental Protection Agency, stressed the importance of proper removal techniques, advising that algae should be uprooted rather than cut to prevent regeneration and unintended spread downstream. While cooler autumn temperatures may reduce growth temporarily, authorities anticipate renewed blooms in the spring.

For now, residents and boating enthusiasts like Romanini acknowledge that adaptation is necessary. “We will have to learn to live with it—and show more respect for the river,” he said, highlighting the changing relationship between the community and this vital waterway amid evolving environmental challenges.