Northern Trust bought Waterline Partners LLC, a Los Angeles investment advisory firm serving affluent individuals and families.

The price of the deal, which closed Wednesday, was not disclosed.

“We are delighted to announce a strategic acquisition that will bolster both our West Coast presence as well as our capabilities for clients,” said Frederick H. Waddell, Northern Trust chairman and chief executive officer. “Waterline is highly regarded for its holistic approach to wealth management, making it an excellent fit with Northern Trust’s client-focused investment strategies.”

Waterline’s founder, chief investment officer and managing partner, Jeffery Coyle, and the entire Waterline team will join Northern Trust. Waterline has $807 million in assets under management.

“Waterline has developed a strong reputation for designing custom investment portfolios that balance clients’ needs for growth, income and preservation of capital,” said Sherry Barrat, president of Northern Trust’s Personal Financial Services business unit. “We are pleased to welcome the clients, partners and staff of Waterline to Northern Trust.”

As of September 30, 2010, Northern Trust’s Personal Financial Services business unit had $149 billion of assets under management and $349 billion of assets under custody.