Blue Harbour Group, an activist investor fund, has amassed a 5.7% stake in Investors Bancorp in New Jersey.

Blue Harbour, in Greenwich, Conn., reported Thursday that it owned about 20.4 million shares of the $17.5 billion-asset Investors as of Aug. 11.

The activist fund has built its holdings over the past several months. Blue Harbour had previously reported that it owned about 15.9 million shares of Investors as of June 30.

Blue Harbor said in a regulatory filing that it has held talks with Investors' management about "strategic alternatives" and plans to hold more talks, and that it "may take other steps seeking to bring about changes to increase shareholder value as well as pursue other plans."

Blue Harbour paid about $212 million to acquire its entire holding of Investors Bancorp, spread out over multiple transactions. Blue Harbour did not own shares in other banks or financial-services companies as of the end of the second quarter.

Investors, in Short Hills, N.J., completed its conversion in May from a thrift that was majority-owned by a mutual holding company, to a fully stock-owned bank. It raised about $2.2 billion through its so-called second-step conversion.

Investors' chief executive, Kevin Cummings, has said he wants to expand the bank to $30 billion of assets in the next five to six years.

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