Investors pulled the most money out of U.S. mutual funds in the week ended August 3 since the depths of the stock market collapse in March 2009, with net redemptions of $16.9 billion, data from the Investment Company Institute showed on Wednesday.

For a second straight week, each major fund category tracked by ICI, a U.S. mutual fund trade organization, showed net outflows of cash, illustrating investor anxiety over future economic growth.

The estimated data does not capture withdrawals after the U.S. credit rating downgrade by Standard & Poor's, which occurred late on Friday, August 5.

Last week's outflows were the most since the week ended March 11, 2009, when ICI reported net outflows of $21.65 billion. The largest net outflow -- nearly $60 billion -- occurred in the week ended October 15, 2008.

Net redemptions of $2.86 billion for fixed income funds was the worst week since late December 2010, while equity funds, with net outflows of nearly $13 billion, had their worst week since late May of last year.

(Reporting by Daniel Bases; Editing by Dan Grebler)