“missing number treated as zero” because of newenvironment

Question

I always get the same errors with these environments. "missing number treated as zero" and "leading text: \begin{satz}" and "Illegal unit of measure (pt inserted)."

\documentclass{article}
\usepackage[utf8]{inputenc}
\usepackage[T1]{fontenc}

\newcounter{satz}
\renewcommand{\thesatz}{\arabic{satz}}

\newenvironment{satz}{%
  \skip%
  \refstepcounter{satz}%
  \textbf{Satz~\thesatz}
}
{% \end{satz}
  \bigskip
}

\begin{document}
\begin{satz}Test\end{satz}
\par
\begin{satz}Test\end{satz}
\end{document}

Anyone knows corrective actions?