Why is it difficult to know the impacts of deep sea mining? It has never been tried successfully, so we don't know exactly how it can be done. It is only done in environmentally sensitive areas, where the organisms are being harmed in many ways already, and it is difficult to know the effects of mining. We know relatively little about deep sea ecosystems, making it harder to assess the impact of mining. Most countries have laws against it, so the impacts have not been tested.