This message is brought to you by Warby Parker.

Their glasses start at $95,

including anti-reflective scratch-resistant prescription lenses

that block 100% of UV rays.

Try five pairs of frames at home for free. Go to Warby Parker.com

slash covered. You're listening to Shortwave from NPR. Hey Shortwaivers, Emily Kwanck here. I'm going to take you back to the mid-80s. A time with some really big boats and some really tiny aquatic

stowaways.

Ian Finkston, who works for the United States Geological Survey, or USGS,

described this for me.

Imagine huge freighters moving upriver, snaking their way from the Atlantic Ocean to the Great Lakes.

Releasing and discharging all their ballast water into the waters of the Great Lakes.

Ballast water. That's what's pumped into a boat to stabilize it before a long journey.

And once the boat gets enough cargo to stabilize on its own, the ballast water can be released.

The thing is, these freighters got their ballast water at a fresh water

port in Eastern Europe, and they dumped that water into the lakes once they arrived.

And unbeknownst to them because it wasn't on anybody's radar, these tiny little bivalves were

entering into the system. These tiny little bivalves, hitchhiking their way to America,

were called zebra Muscles.

And quickly, these Zebra Muscles made their way into the local aquatic ecosystem and took over.

They're basically super effective filter feeders, so they're out competing a lot of the other bi-volves for nutrients

and they were causing impediments and costly infrastructure problems for a lot of the citizens.

It's estimated that zebra mussels annually

...