Above the water line the banks can be fairly flat for easy mowing. Below the water line most recommend 3:1 to discourage weed growth. I have two sides where the slope is 3:1 and two at 5:1 below the water line and have found no significant difference where submerged and emergent plants grow but this is only year 5 for me and I do manage for a weedless pond. Above the water level the banks vary from nearly flat with very moderat swales for surface drainage to 3:1. If I had it to do over I would have built the 3:1 bank at a more gradual slope for safer mowing. One nice thing about steeper banks is less mud is exposed as the water level drops in dry weather. I think any steeper than 3:1 would be a hazard if someone were to fall in because 3:1 is about as steep as I can climb out of when swimming.



"The greatest enemy of knowledge is not ignorance, it is the illusion of knowledge." Stephen W. Hawking