The decision announced on Thursday outlaws fishing in sections of the river that run through the cantons of Jura, Basel-Country and Solothurn, as well as neighbouring France.
The environment office of the canton of Jura said the ban was introduced after a night-time check of the river, which runs along the French border for 12 kilometres and eventually empties into the Birse River in Basel-Country.
Scientists have concluded the river is completely contaminated by crayfish plague, a mold that infects crayfish, killing them within a few weeks.
On Monday, Basel-Country’s department of health and the economy ordered fishers using the Lucelle River to disinfect their rods, tackle and other equipment before fishing in other rivers.
The concern is that the crayfish plaque will spread to other rivers.
The Jura cantonal environment office said it was “counting on all citizens not enter under any pretext into the river bed of the Lucelle,” the ATS news agency reported.
The office added that it is imperative that animals, such as dogs, not bathe in the river, which is known in German as the Lützel.
Experts from the three cantons and the Haut-Rhin department of France will be monitoring the evolution of the mold and the mortality of crayfish in the coming weeks.
The source of the mold has not yet been identified.
No method of combatting the mold is known to exist, according to ATS.
The white-clawed crayfish, found from Sapin to the Balkans, is an endangered species and the only kind of crayfish native to the British Isles.