Yes, underwater turbines are a good idea, because they can create green energy in an economically efficient way, while having little impact on the environment around them. Sometimes, ships sink, but that has never destroyed the marine ecosystem. Marine life will be able to adjust to water turbines just fine.
Yes, underwater river turbines are a good idea, because they produce energy at a reasonable cost. However, it is very important that they are implemented in a humane way and kept away from wildlife and fish. If that is done, and there is a way to produce energy, the impact to the environment is much less than using fossil fuels or other methods of making energy.