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Freshwater ecosystems are currently amongst the most threatened habitats due to high levels of anthropogenic stress and increasing efforts are required to monitor their status and assess aquatic biodiversity. Biomonitoring, which is the systematic measurement of the responses of aquatic biota to environmental stressors, is used to evaluate ecosystem status. Macroinvertebrates are commonly used organisms for ecosystem assessment, due to their numerous biomonitoring qualities, which qualify them as ecological indicators. Traditional taxonomy-based monitoring is labour intensive, which limits the throughput, and is often inefficient in providing species level identification, which limits the accuracy of detections. The introduction of molecular based methods for biomonitoring, especially when coupled with High Throughput Sequencing (HTS) applications, offers a step change in ecosystem monitoring. Here I tested the utility of DNA based applications for increasing the efficiency of freshwater ecosystem biomonitoring, using benthic macroinvertebrates as a target group. For the first part of this work, I used DNA barcoding of the Cytochrome Oxidase Subunit I (COI), from individual specimens, to populate a barcode reference library for 94 species of Trichoptera, Gastropoda and Chironomidae from the UK. Then, I used High Throughput Sequencing (HTS) methods to characterise diversity from complex environmental samples. First, I used metabarcoding of aqueous environmental DNA (eDNA) and community invertebrate samples (Chironomidae pupal exuviae), collected on regular intervals throughout a year, to identify diversity levels and temporal patterns of community variation on ecosystem-wide and group specific scales. Finally, I used a structured design of mock macroinvertebrate communities, of known biomass content, to perform a comparison between PCR-based metabarcoding of the COI gene and PCR-free shotgun sequencing of mitochondrial genomes (mito-metagenomics), and evaluate their efficiency for accurate characterisation of biomass content of bulk samples. Overall, HTS has demonstrated great potential for advancing biomonitoring efforts, allowing ecosystem scale diversity detection from non-invasive types of samples, such as eDNA, whilst moving into mito-metagenomic work could improve the field even further by improving quantitative abundance results on the community composition level.