Stream occupancy of young-of-year arctic grayling (Thymallus arcticus) and the associated impact from the wastewater treatment facility in Baker Laker, NunavutCurrently, the Hamlet of Baker Lake uses a passive wastewater treatment system, where wastewater is released through a series of tundra ponds/lakes and into Baker Lake. This type of system, which is common in Northern communities, takes advantage of natural biological processes and is only capable of providing primary treatment. As a result, relatively high levels of nutrients are released into the system, which can ultimately affect fish and fish habitat. Based on significant positive feedback from the community, an upgraded wastewater treatment facility is anticipated to be constructed in Baker Lake in 2020. These upgrades should improve the quality of water released to downstream systems. A research study is being initiated to study the ecosystems that receive wastewater effluence both before and after wastewater treatment upgrades. Results will help: i) assess current impacts of wastewater on water quality, fish, and fish habitat; ii) determine improvements brought about by treatment upgrades; and, iii) aid in developing a long-term monitoring program. This project proposed here is a component of the larger wastewater treatment study that focuses on recently hatched (young-of-year) Arctic Grayling (Thymallus arcticus). We will:•Compare streams within the wastewater treatment system to reference streams in the region, looking at habitat use of young-of-year arctic grayling, as well as differences in habitat quality and quantity;•Compare fish presence/absence in the wastewater system streams both before and after facility upgrades to assess what impact facility upgrades have on fish habitat; and•Define suitable stream habitat for juvenile arctic grayling, identifying key variables that influence fish presence (e.g., cover, velocity, turbidity, distance to lake habitat, etc.).Research activities will take place in streams within the wastewater treatment system and in suitable reference streams in the region. Within the wastewater system, streams to be sampled include those within the catchment of Lagoon Lake, Finger Lake, and Airplane Lake, as well as the stream connecting Airplane Lake to Baker Lake, as identified on the project map. Reference streams in the surrounding region will be selected based on both suitability and ease of access. It is anticipated that most sites will be within proximity to the all-weather road between Baker Lake and Amaruq. Surveys for young-of-year Arctic Grayling will involve streamside visual observation. These surveys are strictly visual, and no fish are captured. Stream habitat data are collected following each fish presence survey. Variables to be collected include: stream velocity, stream depth, stream width, water temperature, substrate, percentage of in-stream and overhanging vegetation, etc. These variables may affect whether Arctic grayling young-of-year inhabit the stream and/or affect the observers’ ability to detect them. No materials will be moved or removed.These activities, which are completed by a team of two, are anticipated to take approximately 15 days in the field each year, from 2018 to 2021. Transportation will vary among sites, and will include a pick-up truck, helicopter, and/or boat, as appropriate.This research will help characterize the current impact of the wastewater treatment facility on fish, and allow us to monitor changes after treatment upgrades. Results will be highly relevant to other Northern communities as they consider upgrading their passive wastewater treatment facilities.