When attempting to use Cartopy to plot rivers, I'm getting a URL error. I'm not even sure the rivers feature will plot what I want...I'm attempting to get the Galveston Ship Channel to show on my map.

Here's the error I get:

C:\ProgramData\Anaconda3\lib\site-packages\cartopy\io\__init__.py:260: DownloadWarning: Downloading: https://naciscdn.org/naturalearth/10m/physical/ne_10m_rivers_lake_centerlines.zipwarnings.warn('Downloading: {}'.format(url), DownloadWarning)
Traceback (most recent call last):File "C:\ProgramData\Anaconda3\lib\urllib\request.py", line 1354, in do_openh.request(req.get_method(), req.selector, req.data, headers,File "C:\ProgramData\Anaconda3\lib\http\client.py", line 1255, in requestself._send_request(method, url, body, headers, encode_chunked)File "C:\ProgramData\Anaconda3\lib\http\client.py", line 1301, in _send_requestself.endheaders(body, encode_chunked=encode_chunked)File "C:\ProgramData\Anaconda3\lib\http\client.py", line 1250, in endheadersself._send_output(message_body, encode_chunked=encode_chunked)File "C:\ProgramData\Anaconda3\lib\http\client.py", line 1010, in _send_outputself.send(msg)File "C:\ProgramData\Anaconda3\lib\http\client.py", line 950, in sendself.connect()File "C:\ProgramData\Anaconda3\lib\http\client.py", line 1417, in connectsuper().connect()File "C:\ProgramData\Anaconda3\lib\http\client.py", line 921, in connectself.sock = self._create_connection(File "C:\ProgramData\Anaconda3\lib\socket.py", line 787, in create_connectionfor res in getaddrinfo(host, port, 0, SOCK_STREAM):File "C:\ProgramData\Anaconda3\lib\socket.py", line 918, in getaddrinfofor res in _socket.getaddrinfo(host, port, family, type, proto, flags):
socket.gaierror: [Errno 11001] getaddrinfo failed

And here's the code:

import matplotlib.pyplot as plt
import datetime as dt
import cartopy.crs as ccrs
from cartopy.mpl.ticker import LongitudeFormatter, LatitudeFormatter
import cartopy.feature as cfeature
from metpy.plots import USCOUNTIESship_lon, ship_lat = -94.80234, 29.31221ax = plt.axes(projection=ccrs.PlateCarree())
ax.set_extent([-95.5, -94.1, 28.8, 29.8])
ax.add_feature(USCOUNTIES.with_scale('500k'),facecolor='none', edgecolor='gray',linewidth=0.5)ax.add_feature(cfeature.NaturalEarthFeature('physical', 'land', '10m', edgecolor='black', facecolor='#d4d4d4'))
ax.add_feature(cfeature.NaturalEarthFeature('physical', 'ocean', '10m', facecolor='lightblue'))
ax.add_feature(cfeature.NaturalEarthFeature('physical', 'rivers_lake_centerlines', '10m', facecolor='lightblue'))ax.set_title('Hunter-T Approximate Location at Time of Incident',loc='left',fontsize=10,fontweight='bold')
plt.scatter(ship_lon, ship_lat, marker='*', color='black',s=12, zorder=10)
plt.text(ship_lon, ship_lat+.03, 'Vessel Location', fontsize=5, fontweight='bold',horizontalalignment='center')plt.savefig(fname='vessel_location.png',bbox_inches='tight', dpi=600)
plt.close()

If I leave the rivers line out, this is my output. The marker with the vessel location is actually a ship channel. I'm trying to get that body of water to display. I tried searching for a shapefile, but I'm unsure of what shapefile might plot that feature. Or is there a better way to go about plotting a high-res map of this area?

You can try the url it prints in the warning in a browser, and that'll show that it's simply not available at that location. It is when you change https to http. You could try to download and extract it manually to the location as shown in cartopy.config['data_dir'].

But it's probably best to simply update your cartopy version, since it should be downloading the Natural Earth data from AWS, for example from:
https://naturalearth.s3.amazonaws.com/10m_physical/ne_10m_rivers_lake_centerlines.zip

When using cartopy version 0.19 it works fine for me. You do however probably want to change the facecolor to be "none" and only set the edgecolor for the rivers. Since it will otherwise plot the line as if it's a polygon/patch.

ax.add_feature(cfeature.NaturalEarthFeature('physical', 'rivers_lake_centerlines', '10m', linewidth=2, edgecolor='lightblue', facecolor='none',),
)

Zooming out a little to show the rivers more clearly, for me it looks like: