The world's largest hedge fund is struggling

Bridgewater Associates, the world's largest hedge fund firm, is seeing multi-billion dollar swings in performance.

The firm's flagship Pure Alpha fund fell about 12% this year through June, the Wall Street Journal and Institutional Investor's Alpha reported Wednesday.

Different Bridgewater investors are seeing different permutations of that negative performance, since the mega hedge fund creates variations of the strategy for its investors.

For instance, one Bridgewater investor was down 4.6% in its Pure Alpha strategy for June and 7.5% year-to-date, according to a person familiar with the matter.

It's unclear exactly how Pure Alpha performed after the Brexit news last month, though some of its holdings may have helped, the person said.

Pure Alpha was short the British pound, which helped the strategy after the Brexit shock, but was also long European and Japanese equities, which declined, the person said.

Ryan Fitzgibbon, a spokesperson for Bridgewater at external PR firm Prosek Partners, declined to confirm the figures or comment.

It's unclear how much money Bridgewater has lost this year, especially since the firm's All Weather fund, another popular strategy, is up about 10% over the same period, according to the Journal and Institutional Investor reports.

However, Bridgewater has recently seen a slide in assets. A regulatory filing shows that last year, the firm's assets dropped from $169 billion to $152 billion.

To be sure, the hedge fund still trounces its competitors in size. Public pensions, some of the industry's biggest backers, are more likely to be invested in Bridgewater than any other hedge fund, according to data tracker Preqin.

The firm's founder, Ray Dalio, is one of the hedge fund industry's best paid managers, and took home more than $1 billion last year.