What are the avenues and solutions that can significantly reduce the environmental impacts of hydropower plants?

It is well known that large and mega hydropower projects while having the capability to produce renewable power on large scales, have adverse impacts on the neighbourhood ecosystems. What are the concepts, technologies and solutions through which the adverse environmental impacts of hydropower can be significantly reduced?

How will it have a positive impact?

Better Health of Planet

Who will it have a positive impact on?

Government

Highly Vulnerable Entities - Islands, Endangered Species