Flemish Waterways Hit Record Temperatures This Summer

Flemish rivers, canals, and lakes recorded their highest July water temperatures since measurements began, according to data from the Vlaamse Milieumaatschappij (VMM), the Flemish Environment Agency, as reported by RTBF. The unprecedented warmth, driven by a summer of extreme heat and drought, is placing aquatic ecosystems under severe stress and threatening economic disruption for industries that rely on cooling water.

The average water temperature across Flemish rivers and canals in July reached 23.9°C, with specific waterways recording even higher readings. The Grote Nete hit 23.3°C, the Kleine Nete in Antwerp province reached 24.7°C, and the Netekanaal climbed to 25.8°C. All types of watercourses except streams broke their July temperature records, according to VMM thermometers placed throughout the region.

A Summer of Extremes

The record water temperatures are the culmination of an extraordinary meteorological season. Belgium experienced three official national heatwaves between June and August, and summer 2026 is projected to be the warmest since measurements began in 1833, with an average temperature of approximately 20.2-20.3°C, surpassing the previous record of 19.9°C set in 2018, according to the Royal Meteorological Institute (KMI).

Severe drought compounded the heat. July was one of the driest months on record, with just 10.6 mm of precipitation in Ukkel — seven times less than normal. Code orange for drought was declared in Flanders on July 16. With little rainfall to replenish waterways, the remaining water warmed more rapidly.

“We are heading towards the warmest summer since measurements began in 1833,” said David Dehenauw, head of forecasting at the KMI, as reported by VRT NWS. “There’s immediately half a degree more, and that is quite a lot.”

Ecological Stress on Aquatic Life

The warm water is taking a heavy toll on fish populations across Flanders. Gerlinde Van Thuyne, fisheries biologist at the Instituut voor Natuur- en Bosonderzoek (INBO), described the situation as unprecedented, as detailed by VRT NWS.

“In the waterways in my area you can see the big fish just lying under the water surface,” Van Thuyne said. “You can assume that all fish species in Flanders are currently under stress.”

Fish face a double threat: warm water holds less oxygen, and many have no escape route. In Balen, a fish ladder was closed for the first time ever due to poor water quality. Native protected species such as the river lamprey and river bullhead are being pushed out of their upstream habitats by exotic species that thrive in warmer conditions. In the Netekanaal, fishermen have caught cichlids — tropical aquarium fish that normally only occur in Lake Malawi — now surviving in Flemish waters.

“We have really never seen this before,” Van Thuyne said. “So we don’t know what the future brings. We will have to monitor it closely.”

Economic Risks for Industry

Beyond the ecological damage, the high water temperatures pose a significant economic threat. Under Flemish legislation, watercourse temperatures cannot exceed 25°C, a limit designed to protect aquatic life. Companies in the metal sector, chemical industry, data centers, and electricity plants that discharge cooling water could face restrictions or outright bans if the threshold is breached.

“These high temperatures cause ecological damage, but also present an economic risk,” warned Patrick Willems, hydrologist at KU Leuven, as reported by La Libre Belgique. “According to Flemish legislation, the temperature of watercourses cannot exceed 25°C. Companies therefore risk being prohibited from discharging their cooling water.”

Willems noted that companies sometimes discharge water up to 30°C warm into watercourses already at 23°C, which can push temperatures above the legal limit. “In the past we have never exceeded that, but this summer we have come very close in several places,” he said.

The Brussels Times reported that companies may need to invest in cooling technologies such as cooling towers to become more self-sufficient. “A discharge restriction that forces you to temporarily halt production, nobody wants to experience that,” Willems said.

Climate Change as the Underlying Driver

The record summer fits a broader pattern of accelerating climate change. Since 2010, VMM annual average measurements show Flemish waterways have been steadily warming. Climate scientists say this is no coincidence.

“This record summer is no coincidence: our climate continues to warm and records will therefore continue to fall in the coming years,” said Kobe Vandelanotte, climate scientist at the Belgian Climate Centre, as quoted by the KMI. “We must reduce our emissions to stop that, and at the same time adapt to limit the consequences.”

Seawater temperatures in the Atlantic, Mediterranean, North Sea, and the Channel are running 2 to 5 degrees warmer than normal, and that heat does not dissipate quickly, sustaining elevated air temperatures across the region.

What to Watch For

The Flemish government’s Blue Deal water plan aims to make Flanders more resilient to drought and flooding, including measures to retain groundwater that can help keep watercourses cooler during dry periods. However, the effects are largely local, and experts say businesses will ultimately need to invest in their own water management solutions.

As summer 2026 draws to a close, the question is whether the coming weeks bring sufficient rainfall to cool the waterways and relieve the pressure on aquatic ecosystems. With climate projections pointing to more frequent and intense heat events, the record temperatures of this summer may be a preview of what lies ahead for Belgium’s water systems.