Abstract: A needle-beam cofferdam, needles and associated method for dry isolation of a water passage of a dam, the method comprising providing a support beam which spans between piers of the water passage, providing at least one hollow metal needle having a major axis, and positioning the hollow needle with the major axis substantially vertically oriented, the hollow needle engaging with a sill of the dam and engaging with the support beam. A plurality of vertically positioned needles may thereby isolate the water passage. The method also includes positioning of hollow needles with the major axis in a substantially horizontal orientation.