Stablecoins are digital currencies that peg to non-volatile values, such as most commonly fiat currency. Yet unlike fiat currency, stablecoins are fully transparent: every transfer is recorded on a public blockchain. In this regard, they can serve as a valuable case study of the disruptive effect which transparent money flows could have on financial markets. This study analyzes how 1,587 stablecoin transfers of $1 million or more between April 2019 and March 2020 affected Bitcoin returns and trading volume. It finds highly significant positive abnormal trading volume and significant abnormal returns in the hours around stablecoin transfers. The sender and receiver of each transfer are categorized as (1) unknown, (2) cryptocurrency exchange or (3) stablecoin treasury. The effects on trading volume and returns differ across the resulting nine subsamples, which suggests that market participants presume different transfer motives and varying degrees of information asymmetry for each sender-receiver combination. The findings illustrate the feedback effects between cryptocurrency markets and stablecoin usage and suggest that transparent money flows have the potential to increase market efficiency.