Applied and Environmental Science

Humble Hydrogen Peroxide Saves Fish from Algal Blooms

Officials at the Norfolk and Suffolk Broads National Park in the UK hope to bring the park’s fish stocks back to pre-1969 levels when blooms of the algae Prymnesium parvum (golden algae) first decimated the number of pike and other sport fish in the park’s rivers by using hydrogen peroxide to keep the algae in check.  The new tool was found at the John Innes Centre and the University of East Anglia by researchers trying to keep the 100 million pound sport fishing economy of the region in good health.

Since the huge 1969 algae-induced die-off, repeated algal blooms have killed thousands of fish and forced the Environment Agency of Britain to relocate fish at great trouble and expense.  The latest effort, in 2015, involved rescuing almost 750,000 fish from Hickling Broad and Somerton and releasing them back into safer parts of the River Thurne in Norfolk during the next six weeks.  The operation cost almost 40,000 pounds and involved 561 hours of staff time.

Norfolk and Suffolk Broads National Park

Blooms of golden algae happen regularly in the brackish waters of Norfolk and Suffolk; but unfortunately, in spite of their name, these algae are not visible and park staff only know it is there when fish start dying or frantically trying to escape a toxic area.  Helped by a virus, the algae can produce toxins in the water that can kill fish in days and sometimes hours.  Hydrogen peroxide not only kills the algae, it breaks down the toxin as well.

Ben Wagstaff, a student at the John Innes Center who participated in the trials explained that the lab tested peroxide concentrations to find one that would kill the algae but not affect fish or macro invertebrates.  They tested their formula in a small section of one of the rivers that had been affected by golden algae and it worked very well.

The British Environment Agency already uses hydrogen peroxide during pollution incidents to raise oxygen levels for fish and keep them from suffocating, and the chemical can also increase water oxygenation when many fish are trapped in a small area.  Wagstaff said that hydrogen peroxide is the most effective water aeration method by far, and the dose needed to kill off the algae is only slightly higher than the aeration concentration.  After a short period of time, the chemical breaks down into water and oxygen so it is environmentally safe.

Although hydrogen peroxide will also be a boon to fish hatcheries around the world for which Prymnesium parvum is a problem, British conservationists around the Broads National Park are simply grateful that they will be able to keep on “angling.”

Prymnesium is one of the biggest risks to the fish population in the Borads,” said Jamie Fairfull, senior environmental officer for the Environment Agency.  “Being able to use hydrogen peroxide is a major breakthrough because, for us, the current options are so labor intensive.  The Environment Agency usually charges polluters for the cost of dealing with pollution incidents, but with Prymnesium, of course, there is no one to invoice.”

John Currie, general secretary of the Pike Angling Club of Great Britain, said, “It’s hard to put into words how important this is for us.  Thanks to this research…we can save fish rather than observe them dying.  At one time, before the first Prymnesium wipe out in 1969, this area had the British pike record, so [it] was one of the most important pike fisheries in Europe.  With this success we hope that in the next six years we will see growth rates coming back to pre-1969 levels.  That’s completely feasible.”

For more information, go to the web site of the John Innes Center at


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