Watson Lake (Figure 2) is a reservoir created by the Granite Creek Dam along Granite Creek. Watson Lake is subject to a TMDL due to impairments for high nitrogen, low dissolved oxygen, high pH, and experiences fish kills, Harmful Algae Blooms (HAB’s), and aquatic weed blooms (Figure 3). Blooms are due to the excess nitrogen, phosphorus, and organics impounded in the lake, and a buildup of lake bottom muck. These issues manifest largely from May to September. Lake impairments arose out of a history of using effluent water from Sundog WWTP to maintain lake levels, and from pollution loads transmitted by creeks and other drainages from the watershed above. As a result of natural and anthropogenic pollution sources the lake has experienced significant eutrophication. Lake impairments reduce the viability of aquatic habitat, prohibit swimming or full body submersion into Watson Lake, and reduce recreation income and public use. Under the previous management, Chino Valley Irrigation District, the lake was regularly drained and dredged to prevent the issues described above. Under the management plan of the City, draining the lake is not feasible and dredging is not affordable. The City of Prescott seeks a qualified vendor to perform whole-lake treatments and management to reduce excess nutrients and mitigate HAB’s, weeds, low dissolved oxygen, as well as high pH. The firms suggested treatment method/product should result in significant improvements to lake water quality. Water testing shall be conducted before, during, and after treatments to demonstrate effects and/or evaluate the need for adjustments. The firm is to provide any application tools, hardware, or systems needed to dispense product, and any boat or other vessel to be used for that purpose. The firm shall also welcome relevant city staff to be present during treatment for the purpose of basic oversight and education. The Watson Lake Enhancement Plan envisioned by the City will include the following items: 1) Identify the product firm would use to treat lake for excess phosphorus reduction on the order of 50% or greater. 2) Describe the treatment application method and basic treatment plan including how and where the treatment product would be dispersed 3) Recommend number and timing of water quality treatments to achieve target results. Provide a best estimate of the number of days a treatment would require. 4) Note any anticipated disruption to lake recreation, or any need/suggestion for closure or restriction of public access. 5) Describe if or how the proposed treatment may affect aquatic life and the general atmosphere of the lake. For example, should the City expect changes in water clarity or color, odors, bubbling, or other side effects the public should be made aware to expect? 6) Outline timing and scope of water testing to demonstrate treatment protocol is effective. Adjust treatment product application rate or timing as needed, upon written agreement with the City’s project manager
