Eurasian Watermilfoil (Myriophyllum spicatum) is a submerged aquatic plant with a complex impact on freshwater ecosystems. While it can offer some limited benefits, its invasive nature predominantly poses significant threats to biodiversity and waterbody function. Understanding both sides of this “double-edged sword” is crucial for effective management.  

Limited Benefits in Specific Contexts:

In some instances, particularly at low densities, Eurasian Watermilfoil can provide underwater habitat for certain fish and invertebrates. Its dense foliage can offer shelter for small fish and fry, potentially increasing their survival rates. Additionally, it can contribute to oxygen production through photosynthesis, although this benefit is often overshadowed by the negative impacts of large infestations. In heavily managed systems where native plants are scarce, it might temporarily serve as a food source for some wildlife, though its nutritional value is generally lower than that of native species.  

Significant Threats to Ecosystems:

The invasive characteristics of Eurasian Watermilfoil lead to a multitude of detrimental effects:

• Reduced Native Biodiversity: Its rapid growth and formation of dense surface mats outcompete native aquatic plants for sunlight and nutrients, leading to a decline in native plant diversity and abundance. This, in turn, disrupts the food web and reduces habitat for native fish and wildlife.  
• Impeded Water Flow and Navigation: Thick mats can obstruct waterways, hindering boating, fishing, and swimming. They can also impede the flow of water in irrigation canals and flood control systems.  
• Decreased Water Quality: Dense stands can lead to oxygen depletion as the plant decomposes, potentially causing fish kills. They can also alter water temperature and contribute to increased sedimentation.  
• Increased Mosquito Habitat: Stagnant water trapped within dense milfoil mats can create ideal breeding grounds for mosquitoes, increasing the risk of disease transmission.  
• Impacts on Recreation and Economy: Dense infestations can severely limit recreational activities, leading to economic losses in tourism and reduced property values.  

The Verdict: Predominantly a Threat:

While Eurasian Watermilfoil may offer minor, localized benefits, its aggressive growth and invasive nature overwhelmingly result in negative ecological and economic consequences. Its ability to rapidly colonize new areas through fragmentation makes eradication extremely difficult and costly