The rainbow trout Oncorhynchus mykiss has been introduced in at least 97 countries and thus is the most broadly distributed salmonid fish in the world. Native to North America, it was introduced to Europe at the end of the 19th century. Today, the rainbow trout is a significant component of many fish communities in the alpine region. Nonetheless, their reproductive success and invasive spread has gained little international attention. Here, I summarize quantitative fishing data from 940 sites, each of which had at least one of three salmonid fishes present. Between 1991 and 2010 a total of 86,437 brown trout Salmo trutta, 12,132 grayling Thymallus thymallus and 14,021 rainbow trout were caught. A total of 803 (85%) sites contained juvenile brown trout (N = 36,597), 203 (22%) sites juvenile grayling (N = 3,387) and 317 (34%) sites juvenile rainbow trout. Based on the presence of at least three year classes, brown trout were established in 736 (78%) sites, grayling in 135 (14%) sites and rainbow trout in 231 (25%) sites. A series of logistic regression models tested the predictive power of various hydrological, landscape and biotic variables in predicting the successful invasion of rainbow trout in Austrian rivers. Hydrological variables involving flood frequency, timing, duration and overall variability predicted the invasive success of the rainbow trout correctly with a probability of up to 75%. By including further variables like water temperature, altitude and the presence of other salmonids, the predictive power of the models reached 92%. The presence of adult grayling proved to be a good indicator of suitable habitat for rainbow trout, reflecting the very similar habitat requirements of these two species. Particular geological regions, mostly dominated by limestone deposits, between 300 and 600 meters above sea level with mean water temperatures of 3.5C in January, 12.5C in July and 7.9C annually represented suitable habitat for rainbow trout.