How do I eliminate spam sigup on my wordpress site

I have a wordpress / Buddypress site.... And am having serious issues with spam users signup.... Have tried using Akismet, but it is seemingly not helping matters.

Please who has a idea as to which plugin to use or if anyone has an idea on which other method to use, please share

Solution

When you use a form for users to register you can use a captcha like in all forms, e.g. I use really simple captcha in combination with contact form 7.