A diving ballast (131) is adapted to be fitted to a scuba tank, so as to replace or at least supplement a waist-fitted weightbelt. The diving ballast (131) comprises an elongate flexible strap formed with open-ended weight-receiving holsters (122) therein and a plurality of weights (126) each having expanded ends and a waisted portion (127) defined between the expanded ends. Each weight is of such dimensions in relation to a weight-receiving holster (122) so that the expanded end of the weight can be worked through the holsters so that the weighted portion is held captive within the holster. The expanded end of the weight can only be worked through the holster when the strap is slack and the waisted portion (127) is held captive by the material of the holster when the strap is under tension along its length. The diving ballast extends to a waist-fitted weightbelt of the type described, as well as to an ankle-belt having a similar configuration. The invention further extends to a diving ballast system incorporating all three types of ballast.