SEIS - Eagle Lake Property Owner's Inc.

Recolonization by resistant vegetation is sometimes a function of seed beds and sometimes theresult of expansion of shoreline vegetation. Najas recolonized areas previously overgrown with_Myriophyllum after the drawdown of Candlewood Lake in Connecticut (Siver et al., 1986),apparently from seeds that had been in those areas prior to milfoil dominance. Cattails andrushes are the most commonly expanding fringe species (Nichols and Shaw, 1983; WDNR,1989). Drawdowns to control nuisance submergent vegetation are usually recommended foralternate years to every third year to prevent domination by resistant plant species (Cooke et al.,1993), although drawdown may be practiced at a higher frequency to gain initial control of targetspeCIes.Recreational facilities and pursuits may be adversely impacted during a drawdown. Swimmingareas will shrink and beach areas will enlarge during a drawdown. Boating may be restrictedboth by available lake area and by access to the lake. Again, winter drawdown will avoid mostof these disadvantages, although lack of control over winter water levels can make ice conditionsunsafe for fishing or skating. Additionally, outlet structures, docks and retaining walls may besubject to damage from freeze/thaw processes during overwinter drawdowns, if the water level isnot lowered beyond all contact with structures.Carefully planned water level fluctuation can be a useful technique to check nuisancemacrophytes and periodically rejuvenate wetland diversity. Planned disturbance is always athreshold phenomenon; a little can be beneficial, while too much leads to overall ecosystemdecline. The depth, duration, timing and frequency of the drawdown are therefore criticalelements in devising the most beneficial program.With specific regard to milfoil, drawdown is known to provide some degree of control throughdrying and freezing of overwintering vegetative plant parts. Success is linked to sufficientdewatering of exposed sediments and a weather pattern that promotes drying and freezing.Control of milfoil in the drawdown zone has often been observed. Eradication has rarely beenachieved, however, mainly due to a common inability to lower the water level to the greatestdepth of milfoil occurrence.In the case of Eagle Lake, the existing outlet control is not capable of implementing a drawdownof the extent necessary to sufficiently impact the milfoil population. An annual drawdown ispracticed, and does appear to keep milfoil out of the shallowest areas, but is not able to reducemilfoil densities in deeper waters. Greater drawdown may be possible with extensive outletmodification and possible dredging, but the cost and potential disadvantages do not suggest thisas a preferred approach.DSEIS for Eagle Lake 42 ENSR