Here are my thoughts without going back through the annual and monthly flow records for Old Hickory.
Milfoil and hydrilla on large reservoirs are very hard to control much less eliminate with spraying alone. TVA tried for years on some of the Tennessee River reservoirs without much success. Local control around docks and shorelines will work, but it is a constant maintenance issue.
The thing that really hurts Milfoil is hard winters followed by high flow and turbid water springs. The cold water slows growth and the turbid conditions block light from reaching the new growth and it kills them off. When we have flood years, it can really knock back the milfoil. When we have several beautiful springs (like this year) it can get re-established and then spread quickly. When Wolf Creek Dam and Center Hill Dam repairs are complete, Old Hickory is likely to get less cold spring runoff. This may also improve conditions for milfoil growth.
So the big picture for milfoil in Old Hickory is that it is primarily controlled by weather patterns. When we have several wet years, it can almost wipe it out and then when we get in stable or low flow years, it can rebound. It will need several years in a row to become a fully re-established. Once the milfoil beds are big, they can withstand wider flow conditions. A wet year next year may eliminate the milfoil from Old Hickory for a while again.
From a fishing stand point, most aquatic vegetation is a good thing, but it can be a problem for recreational boating and other lake water uses. As far as largemouth bass go, cold, wet springs are bad for bass reproduction and bad for milfoil. Old Hickory bass will benefit from both the warm, consistent flow springs from producing a good year class and from the growth of the milfoil. It provides cover and forage areas for small fish. After several good years of bass spawns and milfoil growth, the bass fishing will really pick up. Both bass and milfoil populations track the warm, low flow springs.
Hope that help some,
Jim
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