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The interactions between salinity, growth and evapotranspiration (E(t)) were investigated for Typha domingensis Pers. in a greenhouse growth experiment and in Cienega de Santa Clara, a coastal desert marsh in the Colorado River delta in Mexico. Although Typha is often found in brackish as well as fresh water marshes, salinity imposed severe constraints to its growth and distribution. In the 68 day greenhouse experiment, growth was maximal at 1.1 ppt. (control solution), half-maximal at 3.5 ppt. and negligible above 6 ppt.; 75% mortality occurred at 15 ppt. E(t) decreased with salinity in proportion to growth reduction. In the Cienega, T. domingensis was only found in water of 5-8 ppt. or less. When inflow water was 1.0 ppt., Typha E(t) was estimated to be 1.3 times pan evaporation (E(o)), whereas when inflow water was 3.2 ppt,, estimated E(t)/E(o) was only 0.7. An estimated half of the inflow water to the Cienega exited the vegetated portion of the Cienega unused, owing to the salt tolerance limit of Typha. A practical objective of the study was to predict the effect of brine placement from the Yuma Desalting Plant into the Cienega; it was concluded that the resulting inflow salinity of 7-10 ppt. would result in deterioration of the Typha stands owing to excess salinity.