The dollar's deepening slide is making a winner of hedge funds and other speculators who are the most bearish in four years.

The greenback sank to a 10-month low Friday, rounding out its worst week since May, as weaker-than-forecast economic data raised doubts about the prospect of additional Federal Reserve tightening this year. Analysts at banks including Mizuho and Wells Fargo say the dollar's got further to fall as Thursday's European Central Bank meeting approaches.

The euro got a lift last week from news that ECB President Mario Draghi will attend a Fed symposium in August, which spurred bets that he might use the occasion to signal plans for the bank's bond-buying program. Last week also offered a stark reminder of the growing conviction that other central banks will start catching up to the Fed, as the Bank of Canada's first rate hike in almost seven years spurred a surge in the loonie.