A ~100 ka old laminated tufa (freshwater carbonate) deposit from central Greece was studied for evidence of a seasonal origin of the laminae. Annual laminar couplets (6 mm thick) consist of dense β bands of spring–early summer calcified cyanobacterial bushes and porous α bands of autumn precipitated calcite on un-clustered cyanobacterial filaments. This is evidence of likely seasonal palaeoclimate during the last interglacial in Greece. δ¹⁸O variability is explained by seasonal changes in stream water temperature; however, the total range in δ¹⁸O translates to ~6 °C (±1 °C) almost certainly underestimating the likely actual range of ~17 °C. As abrupt changes in δ¹⁸O inferred temperatures (from warming to cooling and vice versa) occur exactly on sharp petrographic lamina boundaries, we infer that mid-summer and mid-winter precipitates are missing. We suggest that when stream conditions (summer drying and winter cold) are unsuited to cyanobacterial substrate development, no tufa build-up occurs. Laminated tufas are thus incomplete records of annual tufa formation, as are the δ¹⁸O based palaeoclimate records they preserve. They require careful petrographic study linked to high resolution sampling for δ¹⁸O to ensure that palaeotemperature ranges are not seriously underestimated.