Update: Good news, bad news: It looks like our sources for this story were mistaken about the nature of the debris floating in the direction of the U.S., so the situation is actually much better than we thought. Salon has a piece about it here. This doesn't mean that there's no problem and that debris and invasive species from Japan won't wash up over the next months and years (some already have), though, but it's not quite the 'floating island' initially feared. Apologies for our mistaken coverage.
Carrying invasive species from Japan...As can be seen in the dramatic footage from the 2011 Tsunami in Japan, a gigantic quantity of debris were washed out to sea. Some of those formed a floating island of junk about the size of Texas, and that island has been pushed by ocean currents for the past couple years, slowly making its way toward North America. According to the National Oceanic and Atmospheric Administration (NOAA), the debris island is about 1,700 miles off the U.S. West Coast.
While tests on debris that have made their way to the U.S. shows they're not contaminated by radiation, they do carry various organisms that could potentially become invasive to the local ecosystems of North Ameirca's Pacific coast. The Oregon State University looked at what was found on a 185-ton dock that washed up and found all of this:
It's easy to imagine that there would be many more species on the Texas-sized junk pile.