Americans avoided television in historic levels over the past week.

CBS, NBC, ABC and Fox together had the smallest number of prime-time viewers last week in two decades of record-keeping, the Nielsen Co. said. Given the dominance of the big broadcasters before then, you'd probably have to go back to the early days of television to find such a collective shrug.

The first week of July tends to be among the slowest weeks of the year in television, with families more engaged in barbecues and fireworks. The problem was magnified this year because July 4th came on Sunday, largely knocking out one of a typical week's biggest viewing nights.

Together, the four networks averaged 18.9 million viewers in the week ended July 4, Nielsen said. During the season, "American Idol" alone usually gets a bigger audience than that.

NBC's "America's Got Talent" is emerging as the summer's most popular show, with its two original episodes last week the only programs to top 10 million in viewership, Nielsen said.

While the biggest broadcast networks are suffering, the Spanish-language Univision is stepping up. Among the closely watched 18-to-49-year-old demographic, Univision finished second only to Fox in prime-time last week.

It's not World Cup soccer that is behind Univision's success -- it's the prime-time telenovelas "Soy tu Duena" and "Hasta Dinero Separe."

For the week, CBS averaged 5.6 million viewers in prime-time (3.7 rating, 7 share), NBC had 4.7 million (3.0, 6), ABC had 4.5 million (2.9, 6), Fox had 4.1 million (2.5, 5), ION Television had 1.1 million (0.7, 1) and the CW had 950,000 (0.6, 1).

NBC's "Nightly News" topped the evening newscasts with an average of 7.8 million viewers (5.2, 11). ABC's "World News" was second with 6.7 million (4.6, 10) and the "CBS Evening News" had 5 million viewers (3.4, 8). NBC's victory margin was undoubtedly stretched because Thursday and Friday night results were not included in the network's average because the Wimbledon tennis tournament.

ASSOCIATED PRESS

TOP 20 SHOWS

1 America's Got Talent, 8 p.m. Wed. (NBC)

2 America's Got Talent, Tue. (NBC)

3 The Bachelorette (ABC)

4 NCIS (CBS)

5 Two and a Half Men (CBS)

6 Wipeout, Thu. (ABC)

7 NCIS: Los Angeles (CBS)

8 Wipeout, Tue. (ABC)

9 The Mentalist, 9 p.m. Thu. (CBS)

10 The Big Bang Theory (CBS)

11 America's Got Talent, 7 p.m. Wed. (NBC)

12 CSI: Miami (CBS)

13 Macy's 4th of July Fireworks (NBC)

14 CSI: Crime Scene Investigation (CBS)

15 Rookie Blue (ABC)

16 Boston Pops Fireworks (CBS)

17 Hell's Kitchen, 8 p.m. Tue. (Fox)

18 The Mentalist, 7 p.m. Thu. (CBS)

19 Lie to Me (Fox)

20 Criminal Minds (CBS)