leak along back fender

I have a 2003 330 CSI convertible. Along the back fender (opposite side of the gas tank) there is a light blackish leak. It seems to be
coming from under the car and as I drive, it sprays up alongside the fender. It has little bits of matter in it, but I have no clue what is happening. Additionally, the convertible top has stopped working, so I'm wondering if the two are connnected. Does anyone have any ideas what this could be? Thanks,
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