During the 1800s, barriers were installed along miles of the United Kingdom’s longest river to aid ships loaded with cargo as they traveled up and down the River Severn. But as in many other places, fish species that once relied on the river for their annual spawning grounds were suddenly unable to return.

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Though the barriers impacted many types of creatures, one was particularly missed: the shad fish. Known for their fine taste and quality meat, both twaite and allis species of shad were once considered among the finest delicacies served at the court of King Henry III. But ever since their river was divvied up for boat travel, the fish were unable to swim upstream to their favored breeding grounds, BBC reports.

“They used to get up to Shrewsbury and the Welsh border in their hundreds of thousands,” Severn Rivers Trust deputy director Mike Morris tells the Shropshire Star. “When the weirs were put in that all stopped. Within three years of these structures going in the shad population stopped going above Worcester.”

Shad aren’t the only fish that have disappeared from upstream sections of the Severn: Atlantic salmon and the European eel once made their homes in the river as well. But without ways to get past the barriers, residents living alongside the river quickly saw their fish stocks rapidly dwindle away, the Press Association reports. But thanks to a new plan to alter the weirs, these fish might soon return to their ancestral homes.

Last week, the U.K.’s Environment Agency and Natural England, which oversees protected sites, announced a plan to open up the Severn’s weirs. By installing fish passes in the barriers, environmental activists hope that shad, salmon and eels alike will start breeding in the same spawning grounds their ancestors used for millennia, according to the BBC.

“After considerable investment, rivers in England are the healthiest [they've been in] 20 years. This is [due] to more than a decade of hard work,” James Bevan, chief of the Environment Agency, says in a statement. “But there is more to do and ambitious projects, such as the Unlocking the River Severn, to remove weirs and help fish migrate are a crucial part of this.”

Getting the fish back to the upper reaches of the Severn won’t be cheap: the plan secured around £16.8 million (about $20.6 million) so far from the Heritage Lottery Fund and the European Union LIFE program. But part of this funding will also go towards revitalizing the connection between local residents and the river in hopes that they and their own descendants will once again look after the Severn as their ancestors did, the Press Association reports.

“Unlocking the Severn is a very rare opportunity to right 150 years of wrongs,” Heritage Lottery Fund trustee Tom Tew tells the Shropshire Star. “It will save a wonderful, but endangered, migratory fish and hugely benefit the River Severn’s wider environmental health.”

With a little bit of luck, King Henry’s favorite fish might once again swim free in the waters of the River Severn.