The System.IO is not permit in algorithm why ?

The sample in Rest Api use the System.IO.MemoryStream

///
/// When we have a new event trigger, buy some stock:
///

public List GenerateFromURL(string url)
{
List events = new List();
byte[] rawData = null;
string line;

using (var wc = new System.Net.WebClient())
rawData = wc.DownloadData(url);

MemoryStream stream = new MemoryStream(rawData);

using (StreamReader sr = new StreamReader(stream))
{
sr.ReadLine();
while ((line = sr.ReadLine()) != null)
{
Weather w = new Weather(line);
events.Add(w);
if (w.errString != "")
Debug("Weather Err:" + w.errString);
}
}

return events;
}


How to find a solution ?