You likely don't need to worry. In fact, your thesis or dissertation (and other scholarship) being openly available can increase readership and citation rates, among other benefits.
Here are some concerns you may have heard, and some evidence for why they are mostly unfounded.
Plagiarism: What if someone takes credit for my work?
The fact that your publicly-available thesis or dissertation might be copied also means that it is easy to find in order to compare texts and check for plagiarism. A work being openly available as soon as possible - and clearly dated and time-stamped - deters plagiarism by providing proof of the earlier appearance of one work compared to another similar work (see Suber 2012; Cirasella and Thistlethwaite 2017).
Predatory publishers: What if someone publishes my thesis in a questionable journal?
We have not encountered any data or anecdotal evidence to justify a concern about predatory publishers taking publicly-available theses or dissertations and publishing them without the author's consent. SFU grad students own copyright in their theses and dissertations; it would be an illegal act of copyright infringement for a publisher to publish one without the author's permission. If you have been contacted by a publisher about publishing your thesis or dissertation, the Library provides information and tools for assessing a publisher or journal.
Ability to publish: Will a publisher reject my manuscript because my dissertation is already available?
A number of surveys of publishers with offices in North America and the UK have found that only a small percentage of publishers across disciplines would outright reject a manuscript based on a thesis or dissertation (see Gilliam and Daoutis 2019; Ramirez et al 2013; Ramirez et al 2014). In most cases an article, chapter or book will be significantly reworked from the earlier version: Harvard University Press has said that "we expect that the final product will be so broadened, deepened, reconsidered, and restructured that the availability of the dissertation is irrelevant."
Still have concerns? Talk to your supervisor or contact the Digital Scholarship Librarians at email@example.com.