Marissa Mayer has been Yahoo’s CEO for nearly two years and in that time she has revamped many of Yahoo’s websites and apps, and has made some major purchases. Most notably, Yahoo bought Tumblr a little over a year ago for $1.1 billion. Now, however, this purchase isn’t looking so good. According to a ComScore report in the Wall Street Journal, traffic to Tumblr has dropped from a peak of 49 million visitors in December to only 42 million in March. If these numbers are accurate, this loss of 7 million visitors would represent a 15% drop. There’s no obvious reason for this big decline, either: Since the acquisition, Yahoo hasn’t done much to change Tumblr, staying true to its promise to not ruin Tumblr. Yahoo has tried to monetize Tumblr and has been struggling to attract advertisers, and this decrease in traffic will not help their efforts.