President Jacob Zuma's approval rating fell to 46 percent in April, from a 55 percent high in February, TNS South Africa said on Monday.
"It was at this time that the e-tolling saga was at its height (but before the judgment on the interdict), concerns about the re-instatement of Lt-Gen Richard Mdluli were growing and the [ANC Youth League president Julius] Malema suspension was finalised," researcher Neil Higgs said in a statement.
After a volatile 2010, the figures, based on surveys of 2000 adults living in seven metropolitan areas in South Africa, were more stable in 2011, averaging 48 percent.
After a rise to 55 percent in February, the figure then dropped to 46 percent in mid-April.
The figures also show that the proportion of people giving a "don't know" response dropped to more usual levels after being high since 2009.
"People are coming to a more definite view of the president after a long period where many people were not sure about him. These previously uncertain people are shifting to the negative category."
Higgs said "unfortunately, political views in South Africa tend to have a strong correlation with race", which the figures bear out.
The latest reading for blacks, after a strong rise in February, show the lowest figure since September 2010.
Approval for Zuma among whites shows a slow downward trend for both readings in 2012 so far. For coloureds, sentiment shifted positively in February, but dropped back in April. For Indians/Asians, the trend was strongly negative.
Overall, the president's approval levels are best in Gauteng (except Pretoria), and poorest in Cape Town and Port Elizabeth.
People aged 18 to 34 are the most positive at 51 percent (unchanged over the past four readings). Those aged 60 and more are the least positive at 30 percent (down from the 40 percent of November 2011 and February 2012).
In terms of language group, the most positive are those whose home language is isiZulu at 67 percent (unchanged over the past four readings).
Women are somewhat more positive than men (49 percent compared with 43 percent).
Approval ratings for Deputy President Kgalema Motlanthe are slightly higher than Zuma's, at 49 percent for April.
Blacks in metropolitan areas shifted more positively towards him since the end of 2011, but other race groups have become slightly more negative.
Younger people are more positive, with 53 percent approval for Motlanthe amongst those aged 18 to 34, compared with 39 percent amongst those over 50.
Amongst black language speakers, those whose home language is isiXhosa are the least positive at 59 percent. Other language groups average 69 percent.
According to TNS, the only major difference between their rating occurs in Soweto, Pretoria and East London.
In Soweto, Motlanthe's approval rating is 68 percent, compared with Zuma's 50 percent; in Pretoria Motlanthe's is 58 percent and Zuma's 39 percent. In East London Motlanthe scored 64 percent to Zuma's 48 percent.
Motlanthe's overall approval rating for October/November 2011 was 47 percent. Zuma's was 48.
Motlanthe's approval rating in November 2008, shortly after he was installed as president, was 36 percent.
Malema was expelled from the ANC last month for a range of party-related conduct infractions. Mdluli was last week removed from his post as police intelligence head in the midst of controversy over withdrawn charges of murder and corruption. He will be shifted to another position in the police.