Environmental DNA (eDNA) techniques have the potential to become useful tools for investigating the distribution and biomass of aquatic organisms. Additionally, Unmanned Aerial Vehicle (UAV) photos have recently been applied to evaluate vegetation cover. We tested the ability of eDNA techniques to evaluate the distribution and biomass of an invasive macrophyte, Egeria densa (Brazilian waterweed). We conducted field surveys in two Japanese rivers to determine the abundance of eDNA from E. densa and compared it with macrophyte coverage by evaluating UAV photographs taken in the summer and winter. We found eDNA of E. densa in all sampled sites, including various sites with no macrophyte coverage, indicating that there was a broad-scale distribution of E. densa eDNA. In summer, we detected a slightly positive relationship between E. densa eDNA and macrophyte coverage. We did not find a clear relationship between E. densa eDNA and macrophyte coverage, probably because of their widespread and dense distribution and the flow of their materials in the rivers. The seasonal differences in the regression may have been caused by the seasonal growing period of E. densa in the summer, with a decline in their biomass in late autumn and winter. We confirmed the ability of eDNA techniques to survey this invasive macrophyte in rivers by comparing results with coverage measurements from UAV photographs.

环境DNA（eDNA）技术有潜力成为研究水生生物分布和生物量的有用工具。此外，无人飞行器（UAV）照片最近已用于评估植被覆盖度。我们测试了eDNA技术评估入侵性大型植物Egeria densa（巴西水草）的分布和生物量的能力。我们在两条日本河流中进行了实地调查，以确定来自大肠杆菌的eDNA的丰度，并通过评估夏季和冬季拍摄的无人机照片将其与大型植物的覆盖率进行了比较。我们发现埃德娜密花香薷在所有抽样地点，包括各种网站，没有大型植物覆盖，表明存在的大尺度分布大肠杆菌eDNA。在夏季，我们检测到大肠埃希菌eDNA与大型植物覆盖率之间存在正相关关系。我们未发现大肠埃希菌eDNA与大型植物覆盖率之间存在明确的关系，这可能是因为它们的分布广泛而密集，并且其物质在河流中的流动。回归的季节差异可能是由于夏季E. densa的季节性生长期引起的，而秋季和冬季后期生物量下降了。通过将结果与无人机照片的覆盖率测量结果进行比较，我们确认了eDNA技术能够调查河流中的这种入侵性大型植物。