Where is the error?

Algebra Level 2

I am performing the following steps to prove $-1 = 1:$

$-1 = i^{2}$
$-1=i \times i$
$-1 = \sqrt{-1} \times \sqrt{-1}$
$-1 =\sqrt{-1 \times -1}$
$-1 =\sqrt{1}$
$-1=1.$

In which step does the error exist?