SUMMARY:Observations on two watercress beds in Kent have confirmed previous findings (Jones&Baker, 1955) that even in comparatively well‐protected beds the coli‐aerogenes content of the water may be high in summer. They have also shown that in spite of circumstances which would lead one to expect pollution, as in the case of one bed, the coli‐aerogenes content can be low in winter. The season appears to influence the content in the water of coli‐aerogenes bacteria, pectate liquefying bacteria and those capable of growing at 37°, but in the case of those growing at 22° other factors can play a more important part, as higher counts were not uncommon in winter. Seasonal effects were less marked with inlet samples; they were less influenced by atmospheric temperature, and little extraneous contamination occurred. Numbers increased as the sampling point moved from inlet