Executive Summary: Introduced salmonids (i.e., Chinook Oncorhynchus tshawytscha and Coho Salmon Oncorhynchus kisutch, Rainbow Trout Oncorhynchus mykiss and Brown Trout Salmo trutta) support important recreational fisheries within the Lake Michigan ecosystem. Historically, these fisheries were thought to be primarily supported by stocking, but recent research indicates that the majority of some salmonid species may be naturally reproduced. Natural reproduction of salmonids is common and well researched in Michigan tributaries to Lake Michigan. Successful salmonid reproduction is known to occur within some Wisconsin tributaries to Lake Michigan, but little is known regarding the abundance and outmigration of fish hatching in these streams. Specifically, anadromous Rainbow Trout (i.e., steelhead) stocked into Lake Michigan are known to exhibit an adfluvial life history, migrating up tributaries to spawn. Wild offspring have been collected in some of these tributaries, but whether these fish successfully outmigrate from these streams into larger tributaries or Lake Michigan remains unknown. The objectives of my research were to determine if: 1) abundance of wild juvenile salmonids (primarily steelhead) varied among selected streams in relation to available spawning and age-0 habitat, 2) wild juvenile salmonids successfully outmigrated from Wisconsin tributaries into Lake Michigan or into larger tributaries, and 3) stream temperature regimes could limit survival of juvenile salmonids in these streams. Six streams considered to have high to moderate potential (relative to other Wisconsin tributaries) for steelhead natural reproduction were selected for my research in consultation with biologists from the Wisconsin Department of Natural Resources. Four of these streams (Fischer, Hibbard, Stony, and Sauk creeks) are tributaries to Lake Michigan and two of the streams (Pigeon and Willow creeks) are tributaries to the Milwaukee and Sheboygan rivers that flow directly into Lake Michigan. Abundance of naturally-reproduced steelhead and Coho Salmon in each stream was estimated by multiple-pass depletion methods using backpack electrofishing equipment. Average abundance among electrofishing transects was extrapolated to stream length to calculate population size for each stream. Habitat assessments included steelhead redd surveys in spring 2017 and age-0 habitat surveys in summer 2017. Passive integrated transponders (PIT) were implanted in juvenile salmonids and PIT tag monitoring systems were constructed at the mouth of 3 of 6 streams (Willow, Stony, and Hibbard creeks) to determine rates of outmigration during fall 2016 and spring through fall of 2017. Temperature data were collected using temperature loggers placed at multiple locations in each stream. Population estimates for individual streams ranged from 84-2,528 juvenile (age-0 and age-1+) steelhead and 0-801 juvenile Coho Salmon. There was not a correlation between redd counts or availability of suitable age-0 habitat and juvenile steelhead abundance. Outmigration was rarely detected on all three monitored streams with outmigration rates ranging from 1.4% 2.9% among streams. Stream temperature rarely or never exceeded the acute thermal limit for steelhead (27°C) among streams. Additionally, stream temperature did not exceed the chronic thermal limit for steelhead (24°C) for long enough periods to be of concern. My results indicate that outmigration of wild juvenile steelhead and Coho Salmon from Wisconsin tributaries to Lake Michigan is minimal, although I was not able to determine outmigration rates during winter months. Moreover, abundance of wild juvenile steelhead and Coho Salmon in Wisconsin tributaries to Lake Michigan is generally low (hundreds to thousands of fish compared to hundreds of thousands of fish produced in many Michigan streams). Relative to the total numbers of fish stocked and wild age-0 abundance in Michigan tributaries, the contribution of wild juvenile steelhead and Coho Salmon from Wisconsin tributaries to adult populations in Lake Michigan is likely minimal. Return of wild steelhead produced in these streams is probably insufficient to maintain fisheries within these streams. Lack of suitable habitat could contribute to relatively low abundance in Wisconsin streams. Large-scale watershed improvement projects may be effective for increasing the amount of suitable habitat, but increases in juvenile salmonid abundance would likely be inconsequential on a lake wide level.