Risk Assessment - Great Lakes Hydrilla Collaborative

Funded by the Great Lakes Restoration Initiative, the Great Lakes Hydrilla Risk Assessment was completed to understand the potential for introduction and establishment of monoecious hydrilla in the Great Lakes Basin and estimate the potential impacts from establishment. The primary objective of the risk assessment was to identify locations in the Great Lakes Basin most vulnerable to invasion based on likelihood of introduction and environmental suitability (see Priority Watersheds below).

What is a Risk Assessment?

A risk assessment is a systematic process for evaluating the potential risks that may be involved in a particular activity, in this case, the introduction and spread of hydrilla.

Other key components of the risk assessment focused on:

Develop a better understanding of the effects of photoperiod, temperature, and interspecies competition on growth of monoecious hydrilla;
Assess the economic, sociocultural, and environmental impacts of hydrilla establishment in the Great Lakes Basin;
Provide recommendations for prevention, early detection, and rapid response to reduce risk of hydrilla spread; and
Identify best management practices (BMPs) for hydrilla control.

Great Lakes Risk Assessment Process

The risk assessment process had four main steps, each of which was important in informing the subsequent step(s) in the process, and required the input of a diverse team of experts, as well as stakeholders.

Key Findings of the Risk Assessment

Summary Report
Full Report
Appendices

The key findings of the risk assessment are summarized below, and include the priority watersheds for the spread of hydrilla, economic and environmental impacts of hydrilla, and recommendations and BMPs for the management and prevention of hydrilla. These findings are important to understand how hydrilla spreads, and to identify the highest priority watersheds with respect to potential for introduction, coupled with an understanding of the impacts of hydrilla, and recommendations and BMPs for management and prevention of hydrilla, all of which are critical to limiting the spread of hydrilla.

For a full discussion of all findings of the risk assessment, refer to the detailed report or the summary report.

Priority Watersheds

Based on the integration of several components of the risk assessment, the top five watersheds in the Great Lakes Basin with the greatest potential for hydrilla introduction were identified. These priority watersheds were identified using the following:

Data on areas with a water depth of less than 25 feet and water temperatures of 68°F or greater for at least two months. These areas were determined to be most suitable habitat for hydrilla to develop dense and problematic infestations.
Results of the distributional modeling, which related known hydrilla occurrences with local environmental conditions to understand habitat requirements and predict habitat suitability.
Results of the dispersal modeling, which predicted the spread of hydrilla into the Great Lakes Basin via recreational watercraft and boat trailers and identified areas at high risk for introduction.

Top Five Watersheds in Great Lakes Basin Predicted by Modeling to Have the Greatest Future Proportion of Hydrilla-Infested Waterbody Area: Southeastern Lake Ontario (1), St. Clair-Detroit (2), Western Lake Erie (3), Southern Lake Erie (4), and Southwestern Lake Ontario (5)

As shown on the conceptual model of potential mechanisms by which hydrilla can spread, transport by recreational watercraft is thought to be the primary means by which hydrilla moves within a waterbody and into new waterbodies. However, other means of transport (i.e., water flow, dredge spoils disposal, intentional release, and waterfowl movement) are possible.

Top Five Watersheds with Greatest Future Proportion of Hydrilla-Infested Waterbodies

Southeastern Lake Ontario
St. Clair-Detroit
Western Lake Erie
Southern Lake Erie
Southwestern Lake Erie

Economic and Environmental Impacts

Known economic and environmental impacts were summarized from literature, and future potential impacts resulting from the introduction and establishment of hydrilla were estimated.

Economic Impacts

The introduction to and establishment of hydrilla in the Great Lakes Basin would generate a significant negative economic impact on individuals and local, regional, and national economies. The negative economic impacts would include both additional costs as a result of the establishment of hydrilla, such as increased dredge disposal costs, costs associated with the removal of hydrilla from water intakes, and the loss of enjoyment from recreational activities, including fishing, boating, and beach use on the Great Lakes.

In order to forecast those economic effects, existing cost data and economic studies were reviewed and utilized. Overall, the economic losses associated with the impacts on recreational fishing, beach use, recreational boating, and commercial navigation are expected to range between $70 million and $500 million annually if hydrilla were to become established in the Great Lakes.

Minimum and Maximum Estimated Annual Economic Loss Associated with the Establishment of Hydrilla in the Great Lakes

The dollar figures shown on the above table are only a small portion of the potential overall economic impact that could occur. These figures only include the value associated with the direct use of the resources (i.e., the value people place on fishing, boating, or going to the beach). None of the larger-scale impacts on the local and regional economies have been included, such as impacts on the tourism industry or the boating industry.

What is the main takeaway of these analsyses? Given the potentially large economic losses that would occur if hydrilla were to become established in the Great Lakes Basin, the costs to implement a prevention and eradication program would be relatively inexpensive in comparison. Any costs spent to prevent the spread of hydrilla into the Great Lakes Basin or to eradicate hydrilla before it becomes established in the Great Lakes Basin would be more than offset by the economic losses avoided.

Costs associated with hydrilla prevention and management are much less than the potential annual economic losses due to the establishment of hydrilla in the Great Lakes Basin.

Environmental Impacts

The Hydrilla Risk Assessment evaluated the range of potential environmental impacts that could result from the introduction and successful establishment of monoecious hydrilla in the Great Lakes Basin. Potential environmental impacts on the Great Lakes Basin from hydrilla were evaluated on a basin-wide basis in terms of what the impacts may be, where in the Great Lakes Basin environmental impacts from hydrilla may occur, and how extensive those impacts may be by the year 2025. This was done through a literature review and GIS desktop analysis. The GIS desktop analysis was conducted to qualify potential ecological impacts in the Great Lakes Basin by combining the findings of the habitat suitability and dispersal modeling. The results of the modeling were reviewed with available spatial data on waterbodies and coastal wetlands, fisheries, and waterfowl and wildlife resources to identify resources potentially at risk within the 18 watersheds that comprise the Great Lakes Basin

Generally, the environmental impacts identified below are likely to be greatest in the more southerly Great Lakes Basin watersheds, where hydrilla introduction potential and habitat suitability are greatest.

Potential Great Lakes Basin Resources Impacted by Hydrilla by 2025

Recommendations and Best Management Practices for the Management and Prevention of Hydrilla

Refer to the Recommendations and Best Management Practices pages for information summarized from the Hydrilla Risk Assessment.