There are several possibilities to make your pond clean. For the top edge you can choose different natural stone finishes, for a swimming pond you should finish with a rounded side.
Below are a few of the possible finishes.
Pond edges
1. Spotted Blue
2. Tibet Olivian Black
3. Mustang
Swimming pools
11. Spotted Blue
12. Tibet Dark Grey
13. Tibet Light Grey
14. Tibet New Black
15. Tibet Olivian Black
12. Tibet Dark Grey
Side wall finishing
21. Black Quartzite
22. Black Slate
23. Grey Quartzite
24. Rustic Sand
25. Rusty Silver
26. Rusty Quartzite
27. Rusty Slate
28. White Marble