Americans will also be impacted. According to Lipper, 14.34 percent of U.S. mutual fund assets are in European stocks, while any investor with a well-diversified global portfolio is likely holding several U.K. and European-based companies.
If all of this volatility has you feeling anxious, and if you're specifically worried about a vote to leave the EU, there are still some portfolio-protecting moves you can make now.
The first steps? Reduce your exposure to European equities and increase your allocation to gold, said Bob Sewell, president and CEO of Bellwether Investment Management in Oakville, Ontario, Canada.
He thinks that a yes vote will hurt markets and that stocks could fall by 10 percent. As a result, he has lowered his exposure to Europe. In April he reduced those holdings by 5 percent and put that money into cash. He now has just a 15 percent allocation to the region.
Others are reducing their exposure, too. ETF.com reported today that investors pulled $11 billion out of the 10 largest European equity ETFs year to date through June 15.
"You have to look at your portfolio and see how much exposure you really have to Europe," he said. "A simple means of hedging would be to just reduce your overall exposure to the region to some degree."
Sewell also increased his exposure to gold, which historically tends to rise in volatile markets. The precious metal has indeed climbed significantly over the last six months: It's up 22 percent since December, likely because of worries over Brexit, he said.