Seasonal growth of Typha latifolia L. stands in five oxbow lakes of the Athabasca River in the boreal forest zone of Alberta, Canada, was monitored by both the harvest technique and double sampling by regression. The technique for calculating mean biomass and variance for the double sampling procedure is described. The relationship between stem weight and height was linear for flowering stems, but a logarithmic transformation of weight was used for the non-flowering stem regressions. Growth began in late May and stems reached maximum weight by mid-August. Stem mortality (up to 14%) was highest at sites with high stem density, but mortality was limited to small stems at all sites. Total biomass of these stems was less than 4% of the peak above-ground standing crop. In nutrient-poor sites, Typha was found on floating organic mats, but in more nutrient rich sites on grounded substrates. Peak above-ground biomass ranged from 456 to 848 g m −2, generally in response to the successional and nutrient status of the oxbow lake. Sites returned to an earlier stage of succession by flooding had larger stems and greater biomass.