Why is the water of Malaga's Guadalmedina river black?

MALAGA city residents and workers are calling for action as the final stretch of the Guadalmedina river turns black and emits an increasingly foul odour.

The dark hue of the water, which currently reflects the city’s buildings like a murky mirror, has triggered a wave of complaints to Sur.

So what causes these issues?

There are several factors for the colour. Firstly, the mouth of the river has been neglected, with tyres, balls, plastic bottles and all kind of waste.

Then, there is the slope of the river, which has been one of the technical stumbling blocks in all studies that have tried to integrate the Guadalmedina into the city.

Another determining factor is the tidal dynamics and the storms, which have been intense these past few weeks. Last but not least, temperatures have been rising, although mildly.

But what specifically makes the water black is slime and mud. Municipal water company Emasa periodically tries to solve this problems with suction machines that clean the bottom. Tests including sludge analysis and pump and slab installation have proved that only periodic cleaning does the job.

What does Emasa do with the sludge after its removal? The Guadalhorce treatment plant applies processes such as pressing and drying to treat, dehydrate and convert it into organic matter, which can sometimes be reused as fertiliser.

A crew of workers carries out the process, usually using backhoes and pumps. The work adjusts to the tide schedules.

In November 2023, an operation was carried out on a stretch of about 50 metres from the river at the height of Centro de Arte Contemporáneo to the mouth. It took the workers a whole week to remove 800 cubic metres of mud.

Every month, Emasa measures the level of sludge. Once it reaches 500 cubic metres, Emasa proceeds to remove it.

Urban waste thrown into the riverbed is deposited in a container and taken to the Los Ruices recycling centre.

"The last cleaning was carried out before Christmas. Normally, we do three or four cleanings a year. Every two weeks, we measure the accumulated sludge and, based on that, we bring the cleaning forward. We schedule it for days with the lowest tide and no rain. Right now, with the kind of days we're having, it's better to wait," Emasa said.