Sea of Galilee fishermen say authorities may have introduced the wrong kind of fish in an effort to curb unwanted algae, a mistake that could affect the quality of one of the country’s key sources of drinking water.

At the heart of the issue is the identity of the species recently released into the freshwater lake for the purpose of devouring a harmful layer of blue algae collecting on the surface, Maariv reported on Thursday.

Silver carp, which feed on algae, have been used for decades to clean the Sea of Galilee of unwanted marine growth. But this year, some local fishermen claim, a slightly different breed, bighead carp, was introduced.

Although the two species look similar, there is a key difference in their feeding habits: Bighead carp not only do not eat algae but feed on some microscopic organisms that do, meaning the carp could encourage the algae’s growth in the lake instead of limiting it.

Menachem Lev of Kibbutz Ein Gev, on the lake’s eastern shore, told Maariv that he and other fishermen became aware of the difference because of the way the two species behave when they are pulled from the water. Whereas silver carp are known for their energetic flapping, he said, the fish more recently caught are, in the words of one fisherman, “apathetic.”

Although the Agriculture Ministry denies there is anything amiss, unnamed sources told Maariv that ministry tests on some of the fish indicated that they were indeed the wrong species.

Israel first began its program for cleaning the lake with silver carp in 1969. Since then, the specialized fish have been farmed at an Agriculture Ministry research station. Authorities monitor the silver carp population in the lake and decide how many new fish should be introduced to maintain sufficient numbers to keep down algae that diminish the water quality. Each year hundreds of thousands of silver carp are released into the lake.

The Agriculture Ministry told Maariv that there is no basis to the claim that the wrong fish were put into the lake. But samples have been sent for more comprehensive testing to confirm the identity of the carp, the report said.