Lake Mary AZGFD

More than 67,000 rainbow trout varying in size from 3 to 18 inches stocked into Lower Lake Mary in this spring.

By Matt Rinker, Senior Aquatic Wildlife Specialist, AZGFD Flagstaff Region

If you have ever fished Lower Lake Mary, you know it is a lake of boom and bust. Some years the lake is full and fishing is great and other years the lake is low or just a meadow. Well, the story of Upper and Lower Lake Mary is directly tied to the history of Flagstaff and its early settlers. Upper and Lower Lake Mary are named after Mary Riordan, the daughter of the wealthy lumber baron Timothy Riordan. The Riordans lived in the Riordan Mansion which is now an Arizona State Park.

Completed In 1904

Construction of the Lower Lake Mary Dam was completed by the Riordans in 1904 with a pipeline providing water to the town of Flagstaff. According to W.H. Power, "Sometime in the spring of 1905 great holes formed in the bottom of the reservoir on the west side of the channel about 1,200 feet from the dam." From 1905-1907, "efforts were made to fill the large holes. A great many loads of rock, brush, and dirt were hauled and dumped into these holes. This, no doubt, stopped some of the flow of water, but the holes still remain and considerable water is lost through them. The only practical way of stopping this flow is to construct a levee around the holes, which would involve the moving of practically 10,000 cubic yards of earth at an approximate cost of $6,000."

In 1907-1910, an attempt was made to mitigate seepage through the sinkholes and a large earthen levee was constructed between the dam and the sinkholes. Eventually, additional sinkholes formed on the lake side of the levee, negating its effectiveness.

Upper Lake Mary Dam

Given the unreliable nature of the Lower Lake Mary water level, the Upper Lake Mary Dam was constructed in 1941 to provide a more permanent water supply for the City of Flagstaff. Today, we better understand the geology of the area surrounding Lower Lake Mary and know that it sits on a layer of Kaibab Limestone and two fault lines, the largest being the Lake Mary Fault (Natural Channel Design Feasibility Study 2018). These are the main reasons why Lower Lake Mary fails to be a permanent lake.

The natural ebb and flow of water levels in Lower Lake Mary are not necessarily a bad thing for fisheries managers. The last time Lower Lake Mary filled and spilled was during the 2005-2006 winter season, but Lower Lake Mary has held enough water to be a fishery 16 out of the last 20 years.