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).