Environmental DNA (eDNA) approaches, which involve the sampling and analysis of DNA directly from environmental samples, have revolutionized the ability to detect species and monitor biodiversity efficiently and noninvasively. Recent work has demonstrated the potential for eDNA to detect intraspecific genetic variation and conduct population genetic assessments; however, the field of eDNA has thus far been limited to the assessment of short mitochondrial markers that may lack the resolution required for detailed population genetic assessments. In this body of work, I explore the potential for eDNA approaches to assess fish species richness, provide population genetic information, and estimate absolute species abundance. I first combine estimates of species richness using eDNA metabarcoding and multiple capture-based sampling methods to determine the allocation of effort and cost that provides the optimal approach for lake-wide species inventories. Moving beyond species detections, I then review the important considerations and types of analyses that are possible when analyzing intraspecific genetic variation from eDNA samples and conduct a simulation experiment to understand the limitations of estimating species abundance with different genetic markers and levels of genetic variation. I then demonstrate successful amplification of nuclear microsatellite markers from eDNA samples in a mesocosm experiment, providing accurate estimates of allele frequencies and abundance of an aquatic invasive fish species, the Round Goby (Neogobius melanostomus). Next, I use these approaches to conduct a field-based population genetics experiment, showing agreement between tissue-based and eDNA-based estimates of allele frequencies and population genetic parameters. Last, I assess the potential for eDNA approaches to estimate Round Goby abundance in natural environments and compare these estimates to benthic images obtained with an autonomous underwater vehicle (AUV). Collectively, these studies indicate that intraspecific genetic variation from nuclear genetic markers can be detected from eDNA samples in both natural and controlled environments and used to estimate population allele frequencies, genetic parameters, and species abundance. However, careful consideration of the challenges and limitations of these approaches are required for eDNA to be reliably used for population monitoring and assessments.