Oyster Shell Recycling
One thing that blew my mind recently was pictures of massive piles of oyster shells, generally gathered from restaurants and combined together - for example, see below image.
The idea is to gather a ton of oyster shells, dry them out for a few months to clean them, then return them back to the river to help new oysters spawn - very important because oyster populations have plummeted from a couple centuries ago. Oysters can be a valuable partner in cleaning rivers, as they can filter a ton of water.
A project that is supporting them is the Billion Oyster Project: https://billionoysterproject.org/
It's fantastic as it works with schools to teach students about their local environment in New York; I'm a little jealous of these students as they get such valuable hands-on experience, but I'm glad that at least someone's doing it across many schools. I wonder if there are similar programs in other places.
I hope they are all of a local variety and that they will not be introducing foreign oysters into the ecosphere.
These are just the shells, and bleached/sterilized by the sun first... I wonder how much of a risk that would pose... but still an important thing to think about!
It likely won't cause any issue, but I know of several places that the zebra mussel has wreaked havoc on dam pipes and and other things, so was just curious.
There isn't a program like this here in my country, though we've got lots of oyster shells here. I would love to join such program. I think I'd be fun.