I wish I had built mine like
@j.w ’s. I have straight sides 18” to 24” deep on a slope with a flag stone cap. It isn’t an unpleasant look but limited by not being able to put plants easily in the pond. I do have a bog filter and I recommend reading up on all the positive things our members have to say about them. Two years, my pond is about the size of yours, and I haven’t touched a thing for the most part. Add water, scoop out leaves once or twice a year early spring and late fall and haven’t feed my fish in weeks, closer to a month. I do not miss the weekly or monthly filter cleaning one bit.