I think there are a couple of things to say. The first is that in some cases species that come in have very direct and very noticeable and very fast impacts. I'll speak to zebra mussels and the impact they have had in populating very quickly and then forming on the intake pipes for water treatment plants and nuclear power facilities. That happened very fast. It required a huge amount of money to chlorinate and remove those zebra mussels from the intake pipes. So that's a really direct effect, and we can look at other jurisdictions and the impact that some of these species have had in other areas of the world.
We also have what we call a risk assessment tool so that we can do a risk assessment and develop models based on how we know species will move in an ecosystem, how they will behave in an ecosystem. We can look to what we see in other parts of the world, and we can actually look at the potential for a species to cause harmful impacts. Tim can probably speak on a more scientific level about risk assessment, but it's a tool that we use in many things. We often don't have 100% certainty. Certainly when we're dealing with new pollutants, for example, we don't know the long-term impacts and, in many cases, when we speak of invasive species, we don't know with 100% certainty.