I intentionally took a radical (but possible) example. A more related likely result is NIMBYs using the precedent to give all other ecosystems 'personhood' and strangling housing development in lawsuits. Now that I consider this, judges could use other creative readings of corporate law to actually weaken environmental law (can we use eminent domain on the river? Does it have a natural monopoly on water supply and we need to apply anti-trust?).

Ultimately this is an improper hack, suborning the law for political ends. There are some evils that can justify even a take-no-prisoners approach. But better protection of river ecosystems? Are there really no better ways to achieve that?

Again, I'm familiar with the "slippery slope to utter catastrophe" line of argument. But here you're not even really making it other than to handwave at the possibility. I get that you don't like this. But all law is a political fiction for political ends, so your horror is not something I share.

If you do have a better way to solve it, I encourage you to give it a try. Let me know how it goes.