Two Cyanobacteria strains, isolated from Hamat Gader hot springs, Israel, were identified as Cyanobacterium aponinum and Gloeocapsa sp. Both organisms are known to have various biotechnological applications. The isolates were examined for growth at various combinations of temperature and salinity, in order to test their suitability to grow under local conditions of the Arava in Israel and to establish a possible effect of salinity on thermotolerance. Growth was measured indirectly using in-vivo OD625 and OD680 of the cultures. Optimal growth temperatures for the two strains were 40-45°C, with 50°C as the cutoff for C. aponinum and 55°C for Gloeocapsa sp. They both thrived across the brackish range and up to seawater salinity, yet while C. aponinum showed no growth in fresh water at any of the temperatures tested, Gloeocapsa sp. showed substantial growth at all salinities. Significant interaction was found between salinity and temperature on both Cyanobacteria in the range tested, indicating a possible hardening effect of salinity on thermotolerance. Under the experimental conditions, both wavelengths proved to be useful tools to estimate growth indirectly.In particular, C. aponinum, proved to be a competetive candidate for growth at relatively high temperatures and salinities for various applications.