Volume and contents of residual water in recreational watercraft ballast systems.
Transient boaters are a known vector of aquatic invasive species. This has led to the establishment of prevention guidance to reduce the risk of most boating activities. However, this guidance may not adequately reduce the risk of invasive species transport in wakeboard boats due to the presence of ballast systems, which may be difficult or impossible for a boater to drain. We documented that these watercraft transport relatively large volumes of residual water (mean water volume 31.7 L) even after drain pumps run dry and that live organisms can be found in residual water for at least a week after use. The amount of residual water found in ballast tanks was variable (range of 1.0 L to 86.8 L), indicating that there may be factors that would allow for more complete drainage of ballast tanks. Analyses of the invertebrate communities from the residual water found that native zooplankton were common in the samples, with two of the watercraft transporting small numbers of dreissinid veligers. Future efforts should identify factors that can reduce the amount of residual water and identify what other invasive species may potentially be transported through this new pathway. Additionally, more effort should be made to better understand the boating behaviors of wakeboard boat users.