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If you are looking for an RFID system that would allow tags to be read underwater, low-frequency (LF) or high-frequency (HF) RFID are your only options. Ultrahigh-frequency (UHF) RFID tags cannot be read underwater since the liquid would absorb the RF energy at that frequency. However, LF and HF tags can be read from a distance of only about 3 feet (1 meter), so you would be unable to read tags that were located 4 or 5 meters above the reader antenna. You would need to find a way to keep the tags within about a meter of the antenna. I suggest you contact RFID Inc. to find out if they can assist you. You might also try Oregon RFID, which has had success in tracking fish by running a loop antenna across streams 200 feet wide. Good luck!
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