Here's a straight-up copy/paste from the CTA's website:
The Chicago Transit Authority (CTA) will provide additional service for spectators heading to the annual Air & Water Show on Saturday, August 20 and Sunday,
August 21. The event will take place along the lakefront from Oak Street Beach to Fullerton with the air and water performances combined into one show beginning at 10 a.m. and continuing until 3 p.m. on both days. The best viewing location will be at North Avenue Beach.
Supplemental bus service will be provided on both days on the #72 North Avenue and #151 Sheridan routes, which operate close to all the activities. #72 buses only will travel as far north as North and Clark instead of continuing east to North Avenue Beach in an effort to avoid traffic congestion.
Customers disembarking at Metra’s Union Station or Millennium Park Station can board #151 buses to Oak Street and North Avenue beaches. The #151 buses also are within walking distance of the Ogilvie Transportation Center and the LaSalle Street Metra station.
Buses on the #145 Wilson/Michigan Express, #146 Inner Drive/Michigan Express and #147 Outer Drive Express routes operate to Michigan and Delaware, within walking distance of Oak Street Beach. Customers also can take the #22 Clark or #36 Broadway routes to North and Clark, which is within walking distance of North Avenue Beach.
Spectators who wish to avoid street traffic altogether can reach the Air & Water Show on Red Line trains from subway stations at Chicago/State or Clark/Division, which are within walking distance of Oak Street Beach.
Customers who take the Pink, Orange and Green lines can ride downtown and transfer to the Red Line at State/Lake. Customers can transfer from the Red Line at North/Clybourn, the Blue Line at Damen or the Brown Line at Sedgwick to connect to #72 buses that will supplement regular service along North Avenue from California to Clark.
Longer trains will operate on the Red, Brown, Blue and Orange lines throughout the weekend. CTA customer assistants will be on hand at all downtown rail stations to assist customers with fare and travel information.
Due to anticipated heavy pedestrian and vehicle traffic, the following bus routes will undergo temporary reroute to adjacent streets: #11 Lincoln/Sedgwick; #22 Clark; #36 Broadway; #73 Armitage; and #151 Sheridan.
As a general rule, buses that operate north and south on Clark will travel on LaSalle between Division and LaSalle. The #151 Sheridan will reroute from Inner Lake Shore Drive to LaSalle between North Avenue and Division. The #11 and the #73 will end trips at Clark/Wilson. Customers are advised to allow extra travel time.