General Impact
G. spilanthoides grows very quickly, and is known to rapidly cover water bodies with a floating mat, excluding other plants and the animals that rely on them. The effects of flooding are made much worse because infestations block drainage channels. Recreational activities, irrigation and navigation may also be affected. Water quality may decline if large amounts of G. spilanthoides die off and rot under water." The authors also report that, "G. spilanthoides poses a significant risk to the health of wetland ecosystems. It can quickly take over wetlands and detract from their environmental value, natural beauty and recreational potential. It is also very difficult to control because it can spread by both seed and vegetative reproduction. Even tiny pieces of vegetation can give rise to new colonies. Because it is found mainly in water, the potential impacts of herbicides on nontarget plants and animals must also be carefully managed (The Department of the Environment and Heritage, 2003). Land Protection (2004) reports that, "G. spilanthoides will invade and degrade natural wetlands, competing strongly with slower growing native plants and affecting wetland birds and other animals dependent upon them."
Location Specific Impacts:New Zealand 
Human nuisance: By modifying habitats and smothering other useful species, G. spilanthoides may displace traditional food sources of value to Maori (Waikato Regional Council, 2005).
Modification of hydrology: In New Zealand it has caused flooding by blocking streams and drainage channels (Department of the Environment and Heritage, 2003).
“It may also impede the flow of water and interfere with water utilisation including navigation and recreational activities” (Waikato Regional Council, 2005).
Reduction in native biodiversity: It has the ability to exclude submerged native flora species (Waikato Regional Council, 2005).
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