Turtle Lake was created as the last glacier retreated from the area approximately 10,000 years ago.  It is rated as shallow prairie lake with 57 percent of lake presently having a depth of  15 metres or less. Turtle Lake has a large surface area for the volume of water it contains with the result that it experiences high rates of evaporation during the summer months.  The result is that Turtle Lake's it's size and depth is never static and varies greatly over time.

During a "normal year" approximately 90% of  "outflow" of water leaving Turtle Lake an is evaporated to the atmosphere and approximately 10% is via the Turtle River.  The prairie climate is punctuated periods of drought and abundant moisture making it the concept of  "Normal" almost meaningless.  

Water levels fall anytime the "outflow" of water from the lake exceeds the "inflow" of  water from its watershed. Water levels rise anytime the "inflow" of water is greater than the "outflow" the the water.  Seasonal variation are be considerable with the seasonal high water level is usually experienced in mid July.

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Turtle Lake is greatly affected by the climatic cycles of the prairies.  During  periods of prolonged multi-year drought the area and volume of the lake decreases and the Turtle River stops flowing.  During such periods evaporation alone equals or exceeds the total inflow from the drainage basin and the water chemistry changes as salts and minerals accumulate in the lake. During the cyclical periods of higher precipitation the area and volume of the lake increases, the chemistry of the lake changes as the salts and minerals accumulated in the lake are released with the increased flows down the Turtle River. 

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In recent times human population living on or near the shores of Turtle lake have increased dramatically. This population has discovered that constantly changing area and volume of Turtle Lake to be disruptive to their lives and property. This disruption has led to many living near the lake to suggest that the water volume in the lake should be "controlled".  Controlling the area and volume of the lake is difficult because humans do not control precipitation, temperature, wind, and climatic cycles that largely determine the water levels of the lake.  Humans can control the outflow of water via the Turtle River by either restricting or increasing its flow. However the "outflow' via the Turtle River is at times non-existent and at other times largely inconsequential to the 'inflow - outflow' water balance.

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