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.
Wwhich decade was that then (more to the point why did they fail to monitor if they were montoring?)
There's a big difference between easy monitoring of peacetime allied country nuclear reactors and monitoring the enrichment program of a country actively attempting to develp weapons grade material in the absence of any binding agreements.
2009--2019 if my understanding is correct. Note that this period does overlap with major sanctions against Iran, and since the IAEA itself later acknowledged the breach of agreements in this period, it's fair to say that the IAEA monitoring was not as effective compared to Western intelligences.
> There's a big difference between easy monitoring of peacetime allied country nuclear reactors and monitoring the enrichment program of a country actively attempting to develp weapons grade material in the absence of any binding agreements.
This doesn't matter, because it does show that countries can hide (or more accurately, delay the detection of) evidences if they are really willing to do so. And the absence of any binding agreements actually gives Japan more incentive to do that.
Do you have a source for these simulations?
[1] https://academic.oup.com/nsr/advance-article/doi/10.1093/nsr...
[2] https://sciwatch.kiost.ac.kr/handle/2020.kiost/43977 (no actual paper available, I inferred its details from [3])
[3] https://english.hani.co.kr/arti/english_edition/e_internatio...
