In the second-biggest weekly jump so far this year, U.S. money market mutual fund assets hit $689.51 billion for the week ended June 7, according to the Investment Company Institute.

The rise in assets, a jump of $13.73 billion or 2.2% from the previous week, was attributed to declining long-term interest rates, said Walter Frank, chief economist for the IBC Money Fund Report.

"The long bond was yielding 6.5%, and the best of the money market funds was yielding 6.5%, so you didn't give up much for the extra safety," he said.

The nation's 688 retail money market funds held $484.42 billion for the week, an $8.18 billion increase from the previous week. The total includes $387.28 billion in taxable funds and $97.14 billion in tax-exempt funds.

Institutional funds closed the week with $205.08 billion in assets, an increase of $5.58 billion. Taxable institutional funds held $179.81 billion, and tax-exempts held $25.27 billion.

The ICI reports the assets of money market funds to the Federal Reserve Board each week and makes this information available to the public.

The highest jump of the year occurred on Jan. 11, when assets increased $16.73 billion to $648.64 billion.

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