Biological invasions are widely recognized as a major driver of global biodiversity loss. The most cost-effective answer is often population eradication, while the number of individuals is still limited. The detection of the invasive species at low densities is essential for eradication success, which can be difficult using traditional methods. Environmental DNA (eDNA) can facilitate the detection and monitoring of invasive aquatic species at low densities and can be more sensitive than traditional sampling. The African clawed frog (Xenopus laevis) is a highly invasive species and has been recorded in several European countries. Some of its main impacts are disease transmission, competition and predation. In Portugal, the species was discovered in 2006 and since 2010, streams of the Lisbon area, suspected or at risk of invasion, are being monitored and removal is ongoing. This program so far succeeded in containing the spread and reduced frog abundance, although total eradication has not yet been accomplished. To evaluate the success of this program, we collected water samples from fifteen sites. We filtered the samples, extracted DNA from filters, and assayed the extracted DNA for X. laevis DNA using quantitative polymerase chain reaction (qPCR). None of the field and laboratory negative controls was positive. From the fifteen sites sampled, five had positive results for X. laevis eDNA: four lotic sites and one lentic site. Local eradication success was evident mainly in lentic habitats, and three potential failures were also identified. Finding X. laevis at one of these sites only after X. laevis eDNA detection was an important contribution of this technique for the success of the control and eradication program. Previous (2014-2019) abundance is related with X. laevis eDNA detection and concentration, but lotic microhabitat (pool or riffle) was not. Velocity and salinity affected the concentration of X. laevis eDNA captured. Our results corroborate other studies that recommend eDNA as a complementary sampling approach to other traditional methods and add to a growing literature that increasingly suggests its suitability as a tool for the detection of invasive amphibians. We list some of the sites where future actions should be intensified. In the future, the success of the control and eradication program will depend on an enhanced cooperation between the counties that comprise the two river basins.