Russians began warning (complaining) about the high levels in May.
Here is an NPR article from March that says Russia had the gates open, but Ukraine was pouring more water into the reservoir.
The NPR article says Russia was keeping the levels low but "The Ukrainian government has tried to stem the flow by releasing water from other Ukrainian-controlled reservoirs along the Dnipro River to refill Kakhovka".
So was it just a case of bad communication? Did Russia close the gates and forget to tell Ukraine to ease up on the dumping from upstream?? Or did Ukraine over-compensate for the flow that Russia was letting happen?
It seems to me that the fact the Russians were warning about high levels means that they had kept the floodgates open, as the NPR article says, and there was no more they could do.