You can trust the IAEA to actually do monitoring, and also believe that monitoring might be not effective enough. The IAEA failed to effectively monitor the Iranian nuclear program for more than a decade, so why should we expect the opposite?
> I feel like anyone should be able to conduct independent testing on water and fish samples from the area.
You have to tap into the wastewater source, which is much more hard to do independently and also why the IAEA had to show up. The wastewater will then be subject to the ocean currents, so the actual effect would be inconsistent and delayed (up to 10 years, according to simulations). At that point nothing could be done about the year-long dump.
