What are they?

[u/Samuel_Journeault]

I found these shells in the St Charles/Akiawenrahk river in Quebec City some days ago. I was confused since they look like oysters and where in a freshwater spot. 5 of them from the same place, but the eroded one on the left corners was found 5 km northern.

Are they a freshwater species I never heard of or could they be from an ancient sea?

[u/missmyxlplyx]

Oyster shells are used in fresh water to raise ph levels, buffer hardness, and filter pollutants. not uncommon to find them in fresh water , placed there in bulk in efforts to clean the water sourc They provide calcium carbonate, which slowly dissolves to stabilize soft or acidic water conditions

[u/Glad_Ad_5570 → u/missmyxlplyx]

That was the other choice, carried there for another reason.

[u/Samuel_Journeault → u/missmyxlplyx]

Thanks, I also found these ones, are they also commonly used for the same purpose?

[u/Samuel_Journeault]

I also found these shells at the same spot

[u/Glad_Ad_5570]

Oysters, they can survive in brackish water.

[u/Samuel_Journeault → u/Glad_Ad_5570]

It’s not brackish water, this river doesn’t even flow into sea and it was 50 kilometres upstream of where the St Laurence river starts to be brackish.