We have carried out a blind H i survey using the Westerbork Synthesis Radio Telescope to make an inventory of objects with small H i masses (between 106 and 108 M(circle dot)) and to constrain the low-mass end of the H i mass function. The survey has been conducted in a part of the volume containing the nearby Canes Venatici groups of galaxies. The surveyed region covers an area on the sky of about 86 deg2 and a range in velocity from about -450 to about 1330 km s-1. We find 70 sources in the survey by applying an automated searching algorithm. Two of the detections have not been catalogued previously, but they can be assigned an optical counterpart, based on visual inspection of the second-generation Digital Sky Survey images. Only one of the H i detections is without an optical counterpart. This object is detected in the vicinity of NGC 4822, and it has been already detected in previous H i studies. 19 of the objects have been detected for the first time in the 21-cm emission line in this survey. The distribution of the H i properties of our detections confirms our ability to find low-mass objects. 86 per cent of the detections have profile widths less than 130 km s-1, and they can be considered dwarf galaxy candidates. The H i fluxes measured imply that this survey goes about 10 times deeper than any previous blind H i survey. The H i mass function and the optical properties of the detected sources will be discussed in future papers.