Species that are considered high risk have a well-documented history of invasiveness in at least one location globally, and a high or medium climate match to the contiguous United States.
The Spiny naiad (Najas marina) is a dioecious rooted aquatic vascular plant found in brackish or highly alkaline ponds, lakes, and coastal and inland marshes on every continent except Antarctica. This species has been introduced outside of its native range and has become established in those areas. The history of invasiveness for Najas marina is high with established introduced populations having negative impacts of introductions. Impacts include obstruction of boating and fishing, fish kills, and reductions in biodiversity. N. marina is occasionally used in aquariums, is edible and is consumed by some, and is used as an indicator species for water quality assessment. The overall climate match for N. marina was high with few areas of low or medium match. Low match was mainly found in the Pacific Northwest and medium in the interior southeast. The certainty of assessment is high due to the abundant biological and impact of introduction information that was found. The overall risk assessment category for Najas marina is high.