Beijing claims foreign intelligence agencies are attaching tracking and monitoring devices to sea creatures to gather information that could expose weaknesses in China's coastal defences.
China accused foreign governments of enlisting sea turtles to create underwater maps of China's coastline in an attempt to steal sensitive data.
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Beijing posted on social media its claim that international spy agencies are using "new types of espionage equipment" fitted to turtles and fish.
"Relatively large marine animals with sensors attached have been discovered in certain waters of China," the Ministry of State Security said, in a section titled "spy turtles, spy fish".
The creatures were found "swimming in a specific area, collecting sensitive data about the marine environment such as water temperature, salinity and ocean current, transmitting it overseas via satellite", it said.
While China did not name any country or agency in particular, it believes the data collected would be used to "identify weak points in China's coastal defences, posing a serious threat to China's national security", according to the ministry.
The ministry urged proper security checks on equipment received from abroad, and called on fishers to report any unusual buoys or devices found at sea.
China has traded espionage accusations with multiple governments in recent years. Beijing denounced convictions of two men in the United Kingdom for spying on Hong Kong dissidents as a "political farce" last month, accusing the country of "erroneous practices."
German police arrested a married couple on charges of spying for China in May, accusing them of seeking information on advanced technology with military uses.
Back in February, French authorities charged four people, including two Chinese nationals, with suspected interception of sensitive military data, Agence France-Presse reported.
Greek military authorities arrested a colonel in the same month on suspicion of providing classified and top secret information to China, according to the General Staff of National Defence.