It seems a river is rendered differently if mapped with a multipolygon than mapped as a closed ways: <img width="1179" height="2556" alt="Image" src="https://github.com/user-attachments/assets/4aef1011-4ddd-4173-9dcf-4c80a36b831c" />
It seems a river is rendered differently if mapped with a multipolygon than mapped as a closed ways: