Some of the world’s biggest money managers are making sweeping changes to their European money-market funds amid expectations of losses for the normally staid investments.

The moves by BlackRock and Northern Trust stem from the European Central Bank's decision in September to cut interest rates into negative territory. The rate cut threatened the profitability of the €93 billion industry of euro-denominated money funds, which are used by large corporations and institutional investors as a place to park cash while earning a small amount of interest.