The water was clear to light green in color with a Secchi disc reading of 9.3 feet. Within the water column, alkalinity ranged from 156 to 180, and pH was 8.6. These values indicate that the water is hard and well buffered. Oxygen levels dropped below 3 ppm between 30-31 feet, effectively prohibiting most fish from using the water column deeper than 31 feet. Secchi disc depths were also 2-3 feet shallower in the historical water quality surveys.
Diamond Lake is a popular recreational lake.
The entire shoreline of the lake and Diamond Island are lined with cottages and homes, except the wetland area near the outlet. There is one marina, and a public boat launch that can accommodate up to 60 vehicles with trailers. During summer months, lake activity is very high, and there have been some complaints from anglers regarding boat traffic. The first fishery survey of Diamond Lake was conducted in 1887. Gill nets were used for 1 night.