Tritium monitoring in the Channel
Its radioactivity makes tritium an easy radioelement to monitor. This map of the Channel shows that tritium activity due to discharges from La Hague does not exceed 5,500 Bq/m3 even though the dilution is not uniform. You would have to drink 10,000 m3 a year of the most polluted water to reach the annual regulatory limit of 1 mSv (this is because of tritium's low radioactive toxicity).
IN2P3 (source IRSN)