Is My Neighbor’s Downspout Draining Toward My Property Illegal?

I'm looking for some advice about my neighbor's downspouts. They have two extensions that channel rainwater directly onto my property. I've attached some photos to illustrate the issue. The water flows over the retaining wall, which I'm not entirely sure is right on the property line, but it definitely affects my lawn and runs alongside my house. During heavy rainfall, I notice significant pooling and it creates a clear runoff path toward my foundation. To clarify, the downspouts aren't hooked to any drainage system and are solely from my neighbor's side. I haven't had a chance to talk to them yet, but I'm planning to. I'm curious about a few things: 1. Is this setup common? 2. Is it potentially against any property or runoff regulations? 3. What can I do if my neighbor insists on keeping it this way? 4. Should I reach out to the city (I'm in Colorado) or report it to my HOA? Any insights or experiences would be greatly appreciated! Thanks!