This story is over 5 years old.

How a Rotterdam Squat Became a Cutting-Edge Farm

Uit je Eigen Stad is a city farm in Rotterdam experimenting with aquaponics: growing vegetables with the help of fish, and vice versa.

In addition to its modern architecture and status as a key industrial port, Rotterdam is awash in roof gardens, farmer's markets, and even urban pig pens. Of the many projects currently staining the city green, the first was a farm known as Uit je Eigen Stad (UJES), meaning "from your own town." Last December, its organisers embarked on an ambitious project: building the largest aquaponics system in Europe.


Aquaponics is a method for raising fish and plants in a single system and has so far been uncommon in Europe. I visited the farm—by bike, of course—to see how it works.

aquaponics rotterdam I

The city farm and restaurant are located in an old building on a former tram shed in the outskirts of Rotterdam. The route to get there takes you through Delfshaven—not exactly the best neighbourhood—before you arrive at the industrial Nieuw-Mathenesse, near the Keileweg (an infamous prostitution destination) and the recently reopened Ferro Dome music venue. The farm is next to the Merwehaven waterside and this place is ugly, even by Rotterdam standards.


There, I meet horticulturist Ivo Haenen, who almost immediately begins to talk about the history of the place. The site was used for fruit and vegetable processing until the late 1980s. After that, it was abandoned and fell into disrepair as a squat, which it remained until the city loaned UJES the property in 2012. The graffiti and other traces of the squatters are only partially painted over now, and the DIY spirit of the place seems not to have disappeared.

The aquaponics project is an extension of UJES's traditional farming methods. In 2012, the Amsterdam-based art gallery and project space, Mediamatic conducted a test to demonstrate the efficacy of aquaponics. Inspired by that, UJES decided to investigate whether it was feasible and profitable to maintain a large-scale aquaponics program that produced both quality fish and plants. UJES tapped Jan Botman, an expert in the field of hydroponics, to help construction the farm's setup.


I had imagined a large, fish-filled aquarium topped with floating plants—but in practice, the fish never encounter any plants. The water for the fish and the plants is connected, but they are kept in different bins.

Haenen takes me to a large glass greenhouse, inside of which are two knee-high ponds. There, neat rows of lettuce and bok choy grow on floating mats. "New plants are put on one side of the pond," he tells me. "Every week they move on and grow further, until they are at the end and can be harvested."

With aquaponics, the fish constantly produce nutrients for the plants, and the plants clean the water for the fish. UJES works with two parallel systems—one with tilapia and another with catfish—both of which have their own nursery growing lettuce and bok choy, though they also experiment with mint.

aquaponics rotterdam E

As we enter another room, I'm blasted by a wall of heat and humidity—the lens of my camera is covered with mist. This is where the tilapia and catfish are raised. The room is filled with large tilapia-filled aquariums on one side, and three large bins for catfish on the other. Against two walls are huge bioreactor tanks that reach the ceiling. "In the tanks live the bacteria," Haenen explains. "The bacteria are needed to convert the fish waste into nutrients for the plants."

"The water in the tanks becomes toxic to the tilapia and catfish, thanks to the ammonia from their own waste," says Haenen. "And the plants can not absorb ammonia as a nutrient." Thus, the waste-filled water flows through a bioreactor, where the bacteria convert the ammonia into nitrate—the same chemical present in plant fertilizer. From the bioreactor, the water flows through the plant ponds, where the vegetables absorb the nitrate. Thus cleaned the water then goes back to the fish. "The bacteria are the reason why we do not use antibiotics," Haenen adds.

aquaponics rotterdam G

The hardest part is keeping the system in balance. On paper, it all works perfectly, but in practice the system is more fragile."The more fish that we raise, the more plants we need to take the waste—and the other way around, too," says Haenen. "We need to keep a close eye on the daily nutrients, waste, temperature, and more."

I ask Haenen if growing vegetables in water alters their flavor. "Basically, no," he says. "But we have only just started, so it remains something to figure out. The flavor of vegetables is more defined by the amount of sunlight, nutrients, and duration of growth, so I think it's pretty much the same." And the tilapia and catfish? "We haven't killed many yet," Haenen says, "but we tried a few in our restaurant."

Haenen then takes me through a graffiti-painted door and into a room that smells very strongly of fungus. UJES cultivates shiitake mushroom here with the help of three students from the Willem de Kooning Academy and the Rotterdam University, who figured out that they can be grown on the leftovers from the aquaponic system.

aquaponics rotterdam F

The vegetables in the aquaponics ponds are currently sown on plastic mats, but can also be sown on hemp mats. After the plants are harvested, the hemp mats can be used to grow mushrooms. After the mushrooms are harvested, the material can then continue to be used as packaging material. Nothing is thrown away here—everything is reused as much as possible.

It all fits into the vision of UJES: do as much as possible yourself, experiment with new techniques, and show people where their food comes from. In addition to cultivating vegetables, fish, and mushrooms indoors, UJES grows many vegetables outside in its fields and in tunnel greenhouses. Now, at the end of the winter, they are still bare, but in a month or two they'll burst with green in this grey place.

aquaponics rotterdam A

Everything that UJES grows is used in its restaurant or sold, partly through a local market and partly through Rechtstreex—a food co-op through which people can order products directly from a farmer. Next season there will also be farmland available for local people to grow their own stuff, supervised by UJES gardeners. "In the Netherlands, it is not often commercially viable to grow vegetables or fruit on a small scale," Haenen explains. "So we want to use some of the fields to teach people gardening. We offer a course, a piece of land, and everything they need, so that people can start right away. "

The contrast between this farm that produces almost everything itself and the ships in the nearby harbour carrying exotic products from around the world couldn't be starker. And that contrast will only become more apparent in the near future.