ehhh, this, to my ignorant eyes, seems like a disturbance for the marin ecosystem.
Unlike evosystem in air and on land, many marian life travel purely by the flow of water. Harvesting these energy from water flow (on a large scale) can potentially change how these creatures flow, hence influence their preditors, which might change the local ecosystems.
On the other hand, this is not the first time we fuck with the ocean, and likely wont be the last. At least this is for a "good?" cause.