The four dams at Horsetooth are to undergo moderization construction over the next 3-5 years. For some time, seepage through a geological formation called the Lykins Formation has been conducting water underneath the reservoir and eventually under Horsetooth Dam. Limestone in the Lykins formation has been the main culprit. Sonar tests done in 1999 indicated places in the reservoir bed where limestone had collapsed or erosion had occured. Until the reservoir was drawn down to dead storage at Horsetooth Dam, these features found on sonar were called 'anomalies.' One of them was confirmed as a sinkhole, one was an erosion gully, and one was left from original construction.