(Bloomberg)  — Municipal money market funds are hemorrhaging cash in advance of rules aimed at reducing the risk of runs on the pools.

Assets have plunged $64 billion since the beginning of the year to the lowest levels since 1999 as investors pulled money from tax-exempt funds in 25 of the last 30 weeks and shifted into ones that buy only government debt. These government-only funds are exempt from SEC rules effective in October that require floating net-asset values and impose liquidity fees and redemption suspensions under certain conditions.

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