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Gyro eradication - Information in English

Here you will find information concerning

  1. the salmon parasite Gyrodactylus salaris (commonly known as the salmon fluke),
  2. the eradication efforts that are going to take place in four rivers in the Driva-region,
  3. what you can do to avoid spreading the parasite,
  4. and the future of sport fishing in this region.



  • Gyro is a parasite living on juvenile salmon and is eating them alive

  • Gyro is an introduced species and has been in the Drivaregion for more than 30 years

  • The Norwegian Government has eradicated gyro already from 33 of formerly 50 infected rivers (as at October 2017)

  • A chemical solution called “CFT Legumine” containing the agent rotenone was used in almost all circumstances to treat infected rivers, but other methods are under development

  • Alternative metods include aluminium sulfate or chlorine based treatments
  • Until now it is not determined which method will be used in the Drivaregion

  • In the river Driva a dam/fish barrier has been built 25 km upstream from the estuary

  • This fish barrier will simplify the chemical treatment of the river

  • Sea trout migrating up to the fish barrier will be genetically tested, disinfected and released above the fish barrier

  • Driva salmon migrating up to the fish barrier will be genetically tested, disinfected and used for the re-stocking program

  • All juvenile salmon above the fish barrier will have migrated out to the sea after six years and thus the upper part of Driva will be free of gyro

  • After these six years the lower part of Driva and the nearby rivers Litldalselva, Usma and Batnfjordselva will be chemically treated in two consecutive years

  • In the following five to six years, the re-stocking program will be carried out

  • Simultaneously, all four rivers will be surveyed for gyro annually

  • The Norwegian Government might open for restricted fishing in the upper part of Driva under certain circumstances

  • If gyro has not been found for five to six years, the rivers in the Drivaregion are considered to be healthy again

  • From start to end the whole treatment will last for 13 to 14 years before the fish barrier can be opened again

  • It would be unwise to remove the fish barrier at once because there will be a risk that gyro will come back as long as there are contaminated rivers in Norway



1. Information about Gyrodactylus salaris (salmon fluke)

G. salaris is a tiny creature measuring less than half a millimeter in length. It uses its claws to attach itself to the skin of young salmon, which it then eats alive. G. salaris breeds prolifically and a young salmon may be host to up to 10,000 individual specimens before it dies. The parasite is often referred to as the “salmon killer” or simply “gyro”.


The effects of this illness are so serious for the salmon that the whole salmon population can disappear completely from the infected rivers. If we do not do something, fishing for wild salmon in Norway could be consigned to the history books. Thus, it is very important that everyone who is out and about rivers and other inland waters knows how to behave. We all have to do our bit to ensure that this parasite does not spread to other rivers.

Almost dead juvenile salmon after gyro-attack

It is believed that G. salaris is widespread in rivers which flow into the Baltic Sea from Finland and Russia and possibly Eastern Sweden. It seems that the Baltic salmon can withstand the parasite better than our own. In Norway, the parasite was first discovered in 1975 after cultivated fish were imported from Sweden. The parasite occurs in four rivers in the Drivaregion: Driva, Litldalselva, Usma, and Batnfjordselva. Gyro was detected in this region for the first time in the year 1980. However, it is likely that the parasite was already established in the 1970s in the rivers Driva and Litldalselva because in the summer 1975 gyro was found in a nearby research facility that had its water intake from the river Litldalselva and their wastewater drainage near the estuary.

The parasite can be spread by fish, equipment and water from infected waterbodies and fish hatcheries. Spreading of the parasite in Norway mostly happened by infected fish that were transferred to other waterbodies. However, the parasite can also be spread through equipment that was used in different waterbodies. G. salaris can survive for several days in damp surroundings, for example in plastic bags, on dead fish, in packaging, and equipment, such as waders, landing nets, and fishing lines. It is not just fishing tackle that can transfer the infection, but also everything else we use in and near freshwater: rubber dinghies, lilos, canoes and kayaks. It is not difficult to get rid of G. salaris - provided you know what to do.


2. Eradication of gyro in the Driva-region

River Driva is a large river where salmon and sea trout can swim about 100 km upstream. The upper part of the river is partially difficult to access, which complicates the treatment of the whole river. It was therefore decided to build a dam (a so-called fish barrier) about 25 km upstream from the mouth to the sea. This fish barrier is intended to prevent salmon and sea trout from migrating to the upper parts of the river. Since the parasite needs salmon as a host and cannot survive long without it, the parasite population ceases after a few years above the fish barrier. This will take about six years since by that time all young salmon, which were growing up upstream of the fish barrier, have migrated towards the sea as so-called smolts. Without salmon - no parasite!

After these six years, the parasite only remains in the lower 25 km of the river. This river stretch with all its tributaries will be treated chemically after this six-year waiting period. However, it is not determined which chemical will be used. So far, in almost all cases a solution containing rotenone has been used. Rotenone occurs naturally in some legumes, and has been used for a long time by fishermen in Papua New Guinea, Mexico, Ecuador and Brazil. Rotenone is toxic to fish, sedating them first, and driving them to the surface. Nowadays rotenone is used on a large scale as a pesticide (against pests and diseases), insecticide (against insects) and piscicide (against fish). Thus, when a river is treated with rotenone, not only will all fish die, but also all water-living insects that breath with gills. However, several scientific studies have shown that insect populations recover quickly after a completed treatment.

Because rotenone is not water soluble, it is applied in a solution called "CFT Legumine". This solution usually contains 3.3 % rotenone - the rest consists of various adjuvants and solvents. Some of these other substances have by them self a harmful effect, both on animals and on humans. However, since only very small doses of "CFT Legumine” are used during a treatment, river water containing "CFT Legumine " is not a threat. We are talking about a concentration of 1 microgram (1 millionth of a gram) "CFT Legumine" per 1 liter of river water. To reach the lethal concentration of the active ingredient in a human, one would have to ingest 320,000 liters of river water per 1 kg body weight. In other words, an average person with a body weight of 75 kg would have to drink 24 million liters of treated river water to die because of poisoning. Thus, a chemical treatment of a river with rotenone / "CFT Legumine" represents no health risk to humans and animals - apart from the fish and aquatic insects of course.

In principle, it would even be possible to eat these dead fish and bath in a rotenone-treated river (which some people do!). However, the former is not recommended for ethical and the latter for practical reasons.

To be sure that the population is not going to suffer from health issues because of the chemical treatment, the Norwegian state conducts preliminary tests before the actual chemical treatment in order to determine whether groundwater or drinking water wells are affected by the treatment. For this purpose, an agent (formerly often a dye, today often a non-visible but chemically detectable substance), a so-called tracer, is introduced into the river whose diffusion is then traced. However, it must to be said that rotenone does not penetrate very deeply into the ground before it degrades and therefore becomes harmless, whereas a tracer overcomes these barriers and thus can be detected deeper in the substrate. That is of course only beneficial for such a test.

The construction of the fish barrier in river Driva was started in winter 2016 and it is scheduled for completion in spring 2017. This fish barrier is the largest of its kind, both in Europe, and probably in the world. The width of the dam alone is over 80 meters and the height is about 5 meters. Anchoring structures on both river banks are about 45 meters wide and about 10 meters high. Additionally, a fish ladder is built downstream of the barrier, which will lead all upstream migrating fish in a fish house. Here, all fish will be marked and their species genetically determined. If it is a sea trout it will be released above the fish barrier - this is not a problem because gyro can only survive on salmon in the long run. If it is a Driva salmon, it will be transported to another fish house where it will be used to re-stock the river after the treatment. If, however, it turns out to be an escaped farmed salmon or a hybrid between a salmon and sea trout, it will be killed and hopefully lands on a dinner table.

When the fish barrier will be completed in 2017, one has to wait for six years before starting with the treatment of the lower parts of the river. The treatment will be carried out in two consecutive years. In the following five to six years, re-stocking of the river will be carried out to establish new salmon stocks. During this period, the river will be surveyed for gyro annually, and if at the end of this period gyro cannot be detected, the river is considered to be healthy again. Thus, the whole treatment will take at least 13 to 14 years before the river can be declared gyro-free. After this period, the fish barrier can be opened so that both salmon and sea trout can migrate unimpeded all 100 km upstream again. And with this, nothing will stand in the way for normal fishing and watersports anymore!

The rivers Litldalselva, Usma and Batnfjordselva are relatively small and thus are less problematic with regard to the chemical treatment. In river Litldalselva, it was planed to built an electric fish barrier but after further investigation it was concluded that this will not be necessary. In river Usma, there is already a fish ladder that has been closed for years now and thus preventing fish from migrating upstream. Thus, only the lower section (length: 9 km) needs to be treated. In river Batnfjordselva, no fish barrier is planned, and the river stretch that has to be treated is only about 12 km long.


Fish barrier in river Driva

3. Prevention of spreading the parasite

• Do not release live fish into the wild unless you have permission from the County governor (no: Fylkesmann)

• Do not wash and gut fish anywhere other than where you caught them

• Do not take equipment from one waterbody to another without disinfecting it

• Do not throw water out into another waterbody than the one it was fetched from


4. Sport fishing after 2016 in the Driva-region

The Norwegian legal regulations are unmistakable concerning rivers that are treated against gyro: In general, it is forbidden to fish in such rivers, as well as to practice all other types of watersports!

The Norwegian Environment Agency ("Miljødirektoratet") in collaboration with the County governor ("Fylkesmannen") are responsible for defining fishing rules for each watercourse. They are considering allowing fishing below the fish barrier in 2017 and thereafter, but to what extent is not determined yet. This will probably happen in spring 2017.

The Norwegian Agency for Food Safety ("Mattilsynet") may open for fishing if the fishing rights owner (fishing clubs, landowners) organize the necessary precautions to prevent the spread of infection, including disinfection of equipment.

Any watersport activities can be allowed if the performing sportsmen can demonstrate the necessary prevention of spread of infection by a written statement and a valid identification of their equipment. These stickers will be provided to kayak paddlers in the future.

Already today (i.e. July 2017) there are three disinfection stations both in the lower and upper part of river Driva - several other stations are planned!

Publisert: 19.07.2016 Sist endra: 26.02.2018

Disinfection stations in the Drivaregion

This is a map showing all disinfection stations in the Drivaregion where both anglers and paddlers can disinfect their equipment. This is necessary because of the gyro eradication program in the Drivaregion!

Protected area river Driva - fishing prohibited