Katz, Nannis & Solomon PC has leased 11,800 square feet at the Watermill Center in Waltham.

Fortis Management Group and Conway Office Products also recently renewed leases for 2,269 and 6,124 square feet respectively.

Built in 1984, Watermill Center is a six-story, 206,634-square-foot, Class-A office building. New Boston Fund acquired the property in 2000 and has boosted the occupancy rate from 67 percent to 90 percent. In the past 10 months, New Boston has leased 150,000 square feet of renewals and new tenant signings. In 2013, New Boston spent six months completing extensive upgrades and improvements to enhance the building’s entrance, upgrade the main lobby and add to the amenity base.

Cassidy Turley’s Duncan Gratton, David Campbell and Kate Lien represented New Boston Fund in the transactions. KNS and Fortis were represented by Alex Plaisted of CB Richard Ellis. Conway represented itself.